Memcheck classifies leaks differently depending on if a C program exits with `return` or `exit` Given this very simple C program in `test_return.c` ```C #include <stdio.h> #include <stdlib.h> int main(void) { double *a = malloc(100); return 0; } ``` The following output is given ```bash $ gcc -O0 -g test_return.c -o test_return $ valgrind -s --leak-check=full --show-leak-kinds=all ./test_return ==26141== Memcheck, a memory error detector ==26141== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==26141== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info ==26141== Command: ./test_return ==26141== ==26141== ==26141== HEAP SUMMARY: ==26141== in use at exit: 100 bytes in 1 blocks ==26141== total heap usage: 1 allocs, 0 frees, 100 bytes allocated ==26141== ==26141== 100 bytes in 1 blocks are definitely lost in loss record 1 of 1 ==26141== at 0x4848899: malloc (vg_replace_malloc.c:381) ==26141== by 0x10915E: main (test_return.c:6) ==26141== ==26141== LEAK SUMMARY: ==26141== definitely lost: 100 bytes in 1 blocks ==26141== indirectly lost: 0 bytes in 0 blocks ==26141== possibly lost: 0 bytes in 0 blocks ==26141== still reachable: 0 bytes in 0 blocks ==26141== suppressed: 0 bytes in 0 blocks ==26141== ==26141== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0) ``` But when given this slightly different program in `test_exit.c` ```C #include <stdio.h> #include <stdlib.h> int main(void) { double *a = malloc(100); exit(0); } ``` Instead we get ```bash $ gcc -O0 -g test_exit.c -o test_exit $ valgrind -s --leak-check=full --show-leak-kinds=all ./test_exit ==26180== Memcheck, a memory error detector ==26180== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==26180== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info ==26180== Command: ./test_exit ==26180== ==26180== ==26180== HEAP SUMMARY: ==26180== in use at exit: 100 bytes in 1 blocks ==26180== total heap usage: 1 allocs, 0 frees, 100 bytes allocated ==26180== ==26180== 100 bytes in 1 blocks are still reachable in loss record 1 of 1 ==26180== at 0x4848899: malloc (vg_replace_malloc.c:381) ==26180== by 0x10917E: main (test_exit.c:6) ==26180== ==26180== LEAK SUMMARY: ==26180== definitely lost: 0 bytes in 0 blocks ==26180== indirectly lost: 0 bytes in 0 blocks ==26180== possibly lost: 0 bytes in 0 blocks ==26180== still reachable: 100 bytes in 1 blocks ==26180== suppressed: 0 bytes in 0 blocks ==26180== ==26180== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0) ``` The difference being that with `return` the leak is classifies as "definitely lost" but with `exit` the leak is classifies as "still reachable" even though these programs are identical. According to section 5.1.2.2.3 of the C specification: If the return type of the main function is a type compatible with int, a return from the initial call to the main function is equivalent to calling the exit function with the value returned by the main function as its argument; [...] This means that the two above programs should be equivalent and thus behave in the same manner. Linux 5.4.72-microsoft-standard-WSL2 #1 SMP Wed Oct 28 23:40:43 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux Full `-v` ouptut test_exit.c ``` ==26307== Memcheck, a memory error detector ==26307== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==26307== Using Valgrind-3.18.1-42b08ed5bd-20211015 and LibVEX; rerun with -h for copyright info ==26307== Command: ./test_exit ==26307== --26307-- Valgrind options: --26307-- -v --26307-- -s --26307-- --leak-check=full --26307-- --show-leak-kinds=all --26307-- Contents of /proc/version: --26307-- Linux version 5.4.72-microsoft-standard-WSL2 (oe-user@oe-host) (gcc version 8.2.0 (GCC)) #1 SMP Wed Oct 28 23:40:43 UTC 2020 --26307-- --26307-- Arch and hwcaps: AMD64, LittleEndian, amd64-cx16-lzcnt-rdtscp-sse3-ssse3-avx-avx2-bmi-f16c-rdrand-rdseed --26307-- Page sizes: currently 4096, max supported 4096 --26307-- Valgrind library directory: /usr/libexec/valgrind --26307-- Reading syms from /tmp/tmp.wURL71ZPmz/test_exit --26307-- Reading syms from /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 --26307-- Considering /usr/lib/debug/.build-id/61/ef896a699bb1c2e4e231642b2e1688b2f1a61e.debug .. --26307-- .. build-id is valid --26307-- Reading syms from /usr/libexec/valgrind/memcheck-amd64-linux --26307-- Considering /usr/lib/debug/.build-id/84/fedd9a4c04941b8d123398ad0dd0ebc25c120c.debug .. --26307-- .. build-id is valid --26307-- object doesn't have a dynamic symbol table --26307-- Scheduler: using generic scheduler lock implementation. --26307-- Reading suppressions file: /usr/libexec/valgrind/default.supp ==26307== embedded gdbserver: reading from /tmp/vgdb-pipe-from-vgdb-to-26307-by-dylanb-on-??? ==26307== embedded gdbserver: writing to /tmp/vgdb-pipe-to-vgdb-from-26307-by-dylanb-on-??? ==26307== embedded gdbserver: shared mem /tmp/vgdb-pipe-shared-mem-vgdb-26307-by-dylanb-on-??? ==26307== ==26307== TO CONTROL THIS PROCESS USING vgdb (which you probably ==26307== don't want to do, unless you know exactly what you're doing, ==26307== or are doing some strange experiment): ==26307== /usr/bin/vgdb --pid=26307 ...command... ==26307== ==26307== TO DEBUG THIS PROCESS USING GDB: start GDB like this ==26307== /path/to/gdb ./test_exit ==26307== and then give GDB the following command ==26307== target remote | /usr/bin/vgdb --pid=26307 ==26307== --pid is optional if only one valgrind process is running ==26307== --26307-- REDIR: 0x402aa60 (ld-linux-x86-64.so.2:strlen) redirected to 0x580bcec2 (vgPlain_amd64_linux_REDIR_FOR_strlen) --26307-- REDIR: 0x402a830 (ld-linux-x86-64.so.2:index) redirected to 0x580bcedc (vgPlain_amd64_linux_REDIR_FOR_index) --26307-- Reading syms from /usr/libexec/valgrind/vgpreload_core-amd64-linux.so --26307-- Considering /usr/lib/debug/.build-id/7b/e1c1588ba6713462a4091c80bbb78004f47ba6.debug .. --26307-- .. build-id is valid --26307-- Reading syms from /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so --26307-- Considering /usr/lib/debug/.build-id/ca/411cf3a4b32c9d21bbc464935b0f1af28fb2d8.debug .. --26307-- .. build-id is valid ==26307== WARNING: new redirection conflicts with existing -- ignoring it --26307-- old: 0x0402aa60 (strlen ) R-> (0000.0) 0x580bcec2 vgPlain_amd64_linux_REDIR_FOR_strlen --26307-- new: 0x0402aa60 (strlen ) R-> (2007.0) 0x0484ee30 strlen --26307-- REDIR: 0x4027240 (ld-linux-x86-64.so.2:strcmp) redirected to 0x484fcd0 (strcmp) --26307-- REDIR: 0x402afc0 (ld-linux-x86-64.so.2:mempcpy) redirected to 0x4853840 (mempcpy) --26307-- Reading syms from /usr/lib/x86_64-linux-gnu/libc.so.6 --26307-- Considering /usr/lib/debug/.build-id/69/389d485a9793dbe873f0ea2c93e02efaa9aa3d.debug .. --26307-- .. build-id is valid ==26307== WARNING: new redirection conflicts with existing -- ignoring it --26307-- old: 0x04921ce0 (memalign ) R-> (1011.0) 0x0484e080 memalign --26307-- new: 0x04921ce0 (memalign ) R-> (1017.0) 0x0484e050 aligned_alloc ==26307== WARNING: new redirection conflicts with existing -- ignoring it --26307-- old: 0x04921ce0 (memalign ) R-> (1011.0) 0x0484e080 memalign --26307-- new: 0x04921ce0 (memalign ) R-> (1017.0) 0x0484e020 aligned_alloc ==26307== WARNING: new redirection conflicts with existing -- ignoring it --26307-- old: 0x04921ce0 (memalign ) R-> (1011.0) 0x0484e080 memalign --26307-- new: 0x04921ce0 (memalign ) R-> (1017.0) 0x0484e050 aligned_alloc ==26307== WARNING: new redirection conflicts with existing -- ignoring it --26307-- old: 0x04921ce0 (memalign ) R-> (1011.0) 0x0484e080 memalign --26307-- new: 0x04921ce0 (memalign ) R-> (1017.0) 0x0484e020 aligned_alloc --26307-- REDIR: 0x49247a0 (libc.so.6:strnlen) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4924a60 (libc.so.6:strpbrk) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4924360 (libc.so.6:strcmp) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4942d50 (libc.so.6:wcsnlen) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4925750 (libc.so.6:memset) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x49415c0 (libc.so.6:wcslen) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4925c90 (libc.so.6:memcpy@@GLIBC_2.14) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x49413f0 (libc.so.6:wcschr) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x49242e0 (libc.so.6:index) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x49249e0 (libc.so.6:rindex) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4925620 (libc.so.6:memmove) redirected to 0x483f220 (_vgnU_ifunc_wrapper) ==26307== Preferring higher priority redirection: --26307-- old: 0x04a1c940 (__memcpy_avx_unalign) R-> (2018.0) 0x04850f90 __memcpy_avx_unaligned_erms --26307-- new: 0x04a1c940 (__memcpy_avx_unalign) R-> (2018.1) 0x04852880 memmove --26307-- REDIR: 0x4941470 (libc.so.6:wcscmp) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4925a60 (libc.so.6:stpncpy) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4941a30 (libc.so.6:wmemchr) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x49248b0 (libc.so.6:strncmp) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4925af0 (libc.so.6:strcasecmp) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x49244a0 (libc.so.6:strcspn) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x49414f0 (libc.so.6:wcscpy) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4924250 (libc.so.6:strcat) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4925be0 (libc.so.6:strncasecmp_l) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4925500 (libc.so.6:bcmp) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x492d5f0 (libc.so.6:memrchr) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4927090 (libc.so.6:strchrnul) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4924410 (libc.so.6:strcpy) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4925b90 (libc.so.6:strcasecmp_l) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4924720 (libc.so.6:strlen) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4924950 (libc.so.6:strncpy) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x49259d0 (libc.so.6:stpcpy) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4925470 (libc.so.6:memchr) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4924b80 (libc.so.6:strspn) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4925850 (libc.so.6:mempcpy) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4925b40 (libc.so.6:strncasecmp) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4927000 (libc.so.6:rawmemchr) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26307-- REDIR: 0x4a19790 (libc.so.6:__strrchr_avx2) redirected to 0x484e810 (rindex) --26307-- REDIR: 0x4921120 (libc.so.6:malloc) redirected to 0x4848820 (malloc) --26307-- REDIR: 0x4921460 (libc.so.6:free) redirected to 0x484b210 (free) ==26307== ==26307== HEAP SUMMARY: ==26307== in use at exit: 100 bytes in 1 blocks ==26307== total heap usage: 1 allocs, 0 frees, 100 bytes allocated ==26307== ==26307== Searching for pointers to 1 not-freed blocks ==26307== Checked 108,056 bytes ==26307== ==26307== 100 bytes in 1 blocks are still reachable in loss record 1 of 1 ==26307== at 0x4848899: malloc (vg_replace_malloc.c:381) ==26307== by 0x10917E: main (test_exit.c:6) ==26307== ==26307== LEAK SUMMARY: ==26307== definitely lost: 0 bytes in 0 blocks ==26307== indirectly lost: 0 bytes in 0 blocks ==26307== possibly lost: 0 bytes in 0 blocks ==26307== still reachable: 100 bytes in 1 blocks ==26307== suppressed: 0 bytes in 0 blocks ==26307== ==26307== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0) ``` test_return.c ``` ==26315== Memcheck, a memory error detector ==26315== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==26315== Using Valgrind-3.18.1-42b08ed5bd-20211015 and LibVEX; rerun with -h for copyright info ==26315== Command: ./test_return ==26315== --26315-- Valgrind options: --26315-- -v --26315-- -s --26315-- --leak-check=full --26315-- --show-leak-kinds=all --26315-- Contents of /proc/version: --26315-- Linux version 5.4.72-microsoft-standard-WSL2 (oe-user@oe-host) (gcc version 8.2.0 (GCC)) #1 SMP Wed Oct 28 23:40:43 UTC 2020 --26315-- --26315-- Arch and hwcaps: AMD64, LittleEndian, amd64-cx16-lzcnt-rdtscp-sse3-ssse3-avx-avx2-bmi-f16c-rdrand-rdseed --26315-- Page sizes: currently 4096, max supported 4096 --26315-- Valgrind library directory: /usr/libexec/valgrind --26315-- Reading syms from /tmp/tmp.wURL71ZPmz/test_return --26315-- Reading syms from /usr/lib/x86_64-linux-gnu/ld-linux-x86-64.so.2 --26315-- Considering /usr/lib/debug/.build-id/61/ef896a699bb1c2e4e231642b2e1688b2f1a61e.debug .. --26315-- .. build-id is valid --26315-- Reading syms from /usr/libexec/valgrind/memcheck-amd64-linux --26315-- Considering /usr/lib/debug/.build-id/84/fedd9a4c04941b8d123398ad0dd0ebc25c120c.debug .. --26315-- .. build-id is valid --26315-- object doesn't have a dynamic symbol table --26315-- Scheduler: using generic scheduler lock implementation. --26315-- Reading suppressions file: /usr/libexec/valgrind/default.supp ==26315== embedded gdbserver: reading from /tmp/vgdb-pipe-from-vgdb-to-26315-by-dylanb-on-??? ==26315== embedded gdbserver: writing to /tmp/vgdb-pipe-to-vgdb-from-26315-by-dylanb-on-??? ==26315== embedded gdbserver: shared mem /tmp/vgdb-pipe-shared-mem-vgdb-26315-by-dylanb-on-??? ==26315== ==26315== TO CONTROL THIS PROCESS USING vgdb (which you probably ==26315== don't want to do, unless you know exactly what you're doing, ==26315== or are doing some strange experiment): ==26315== /usr/bin/vgdb --pid=26315 ...command... ==26315== ==26315== TO DEBUG THIS PROCESS USING GDB: start GDB like this ==26315== /path/to/gdb ./test_return ==26315== and then give GDB the following command ==26315== target remote | /usr/bin/vgdb --pid=26315 ==26315== --pid is optional if only one valgrind process is running ==26315== --26315-- REDIR: 0x402aa60 (ld-linux-x86-64.so.2:strlen) redirected to 0x580bcec2 (vgPlain_amd64_linux_REDIR_FOR_strlen) --26315-- REDIR: 0x402a830 (ld-linux-x86-64.so.2:index) redirected to 0x580bcedc (vgPlain_amd64_linux_REDIR_FOR_index) --26315-- Reading syms from /usr/libexec/valgrind/vgpreload_core-amd64-linux.so --26315-- Considering /usr/lib/debug/.build-id/7b/e1c1588ba6713462a4091c80bbb78004f47ba6.debug .. --26315-- .. build-id is valid --26315-- Reading syms from /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so --26315-- Considering /usr/lib/debug/.build-id/ca/411cf3a4b32c9d21bbc464935b0f1af28fb2d8.debug .. --26315-- .. build-id is valid ==26315== WARNING: new redirection conflicts with existing -- ignoring it --26315-- old: 0x0402aa60 (strlen ) R-> (0000.0) 0x580bcec2 vgPlain_amd64_linux_REDIR_FOR_strlen --26315-- new: 0x0402aa60 (strlen ) R-> (2007.0) 0x0484ee30 strlen --26315-- REDIR: 0x4027240 (ld-linux-x86-64.so.2:strcmp) redirected to 0x484fcd0 (strcmp) --26315-- REDIR: 0x402afc0 (ld-linux-x86-64.so.2:mempcpy) redirected to 0x4853840 (mempcpy) --26315-- Reading syms from /usr/lib/x86_64-linux-gnu/libc.so.6 --26315-- Considering /usr/lib/debug/.build-id/69/389d485a9793dbe873f0ea2c93e02efaa9aa3d.debug .. --26315-- .. build-id is valid ==26315== WARNING: new redirection conflicts with existing -- ignoring it --26315-- old: 0x04921ce0 (memalign ) R-> (1011.0) 0x0484e080 memalign --26315-- new: 0x04921ce0 (memalign ) R-> (1017.0) 0x0484e050 aligned_alloc ==26315== WARNING: new redirection conflicts with existing -- ignoring it --26315-- old: 0x04921ce0 (memalign ) R-> (1011.0) 0x0484e080 memalign --26315-- new: 0x04921ce0 (memalign ) R-> (1017.0) 0x0484e020 aligned_alloc ==26315== WARNING: new redirection conflicts with existing -- ignoring it --26315-- old: 0x04921ce0 (memalign ) R-> (1011.0) 0x0484e080 memalign --26315-- new: 0x04921ce0 (memalign ) R-> (1017.0) 0x0484e050 aligned_alloc ==26315== WARNING: new redirection conflicts with existing -- ignoring it --26315-- old: 0x04921ce0 (memalign ) R-> (1011.0) 0x0484e080 memalign --26315-- new: 0x04921ce0 (memalign ) R-> (1017.0) 0x0484e020 aligned_alloc --26315-- REDIR: 0x49247a0 (libc.so.6:strnlen) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4924a60 (libc.so.6:strpbrk) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4924360 (libc.so.6:strcmp) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4942d50 (libc.so.6:wcsnlen) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4925750 (libc.so.6:memset) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x49415c0 (libc.so.6:wcslen) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4925c90 (libc.so.6:memcpy@@GLIBC_2.14) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x49413f0 (libc.so.6:wcschr) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x49242e0 (libc.so.6:index) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x49249e0 (libc.so.6:rindex) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4925620 (libc.so.6:memmove) redirected to 0x483f220 (_vgnU_ifunc_wrapper) ==26315== Preferring higher priority redirection: --26315-- old: 0x04a1c940 (__memcpy_avx_unalign) R-> (2018.0) 0x04850f90 __memcpy_avx_unaligned_erms --26315-- new: 0x04a1c940 (__memcpy_avx_unalign) R-> (2018.1) 0x04852880 memmove --26315-- REDIR: 0x4941470 (libc.so.6:wcscmp) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4925a60 (libc.so.6:stpncpy) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4941a30 (libc.so.6:wmemchr) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x49248b0 (libc.so.6:strncmp) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4925af0 (libc.so.6:strcasecmp) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x49244a0 (libc.so.6:strcspn) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x49414f0 (libc.so.6:wcscpy) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4924250 (libc.so.6:strcat) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4925be0 (libc.so.6:strncasecmp_l) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4925500 (libc.so.6:bcmp) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x492d5f0 (libc.so.6:memrchr) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4927090 (libc.so.6:strchrnul) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4924410 (libc.so.6:strcpy) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4925b90 (libc.so.6:strcasecmp_l) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4924720 (libc.so.6:strlen) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4924950 (libc.so.6:strncpy) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x49259d0 (libc.so.6:stpcpy) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4925470 (libc.so.6:memchr) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4924b80 (libc.so.6:strspn) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4925850 (libc.so.6:mempcpy) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4925b40 (libc.so.6:strncasecmp) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4927000 (libc.so.6:rawmemchr) redirected to 0x483f220 (_vgnU_ifunc_wrapper) --26315-- REDIR: 0x4a19790 (libc.so.6:__strrchr_avx2) redirected to 0x484e810 (rindex) --26315-- REDIR: 0x4921120 (libc.so.6:malloc) redirected to 0x4848820 (malloc) --26315-- REDIR: 0x4921460 (libc.so.6:free) redirected to 0x484b210 (free) ==26315== ==26315== HEAP SUMMARY: ==26315== in use at exit: 100 bytes in 1 blocks ==26315== total heap usage: 1 allocs, 0 frees, 100 bytes allocated ==26315== ==26315== Searching for pointers to 1 not-freed blocks ==26315== Checked 108,032 bytes ==26315== ==26315== 100 bytes in 1 blocks are definitely lost in loss record 1 of 1 ==26315== at 0x4848899: malloc (vg_replace_malloc.c:381) ==26315== by 0x10915E: main (test_return.c:6) ==26315== ==26315== LEAK SUMMARY: ==26315== definitely lost: 100 bytes in 1 blocks ==26315== indirectly lost: 0 bytes in 0 blocks ==26315== possibly lost: 0 bytes in 0 blocks ==26315== still reachable: 0 bytes in 0 blocks ==26315== suppressed: 0 bytes in 0 blocks ==26315== ==26315== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0) ```
This is because when you return the stack frame for main is discarded and "a" is no longer live but when you call exit that stack frame still exists and "a" is still live as a result. I think it would be quite hard for valgrind to figure out that exit had been called and then where to unwind the stack to which is what would be needed to get the two to behave the same.
I don't think that this is a bug and don't see much benefit in trying to change the behaviour. Both reports should be clear enough to find the memory.