Bug 503253

The RISC-V Hardware Probing Interface is non-trivial
https://docs.kernel.org/arch/riscv/hwprobe.html

But at the moment we only have the basic RV64GC instruction set.
Which I believe is what glibc assumes if riscv_hwprobe isn't implemented.

So as a quick workaround we could just "implement" riscv_hwprobe as ENOSYS.

diff --git a/coregrind/m_syswrap/syswrap-riscv64-linux.c b/coregrind/m_syswrap/syswrap-riscv64-linux.c
index e0146f2b0dad..ebf9c3105339 100644
--- a/coregrind/m_syswrap/syswrap-riscv64-linux.c
+++ b/coregrind/m_syswrap/syswrap-riscv64-linux.c
@@ -545,6 +545,7 @@ static SyscallTableEntry syscall_main_table[] = {
    LINXY(__NR_perf_event_open, sys_perf_event_open),               /* 241 */
    LINXY(__NR_accept4, sys_accept4),                               /* 242 */
    LINXY(__NR_recvmmsg, sys_recvmmsg),                             /* 243 */
+   GENX_(__NR_riscv_hwprobe, sys_ni_syscall),                      /* 258 */
    PLAX_(__NR_riscv_flush_icache, sys_riscv_flush_icache),         /* 259 */
    GENXY(__NR_wait4, sys_wait4),                                   /* 260 */
    LINXY(__NR_prlimit64, sys_prlimit64),                           /* 261 */
diff --git a/include/vki/vki-scnums-riscv64-linux.h b/include/vki/vki-scnums-riscv64-linux.h
index e4cc04a608b4..17b6839f8a84 100644
--- a/include/vki/vki-scnums-riscv64-linux.h
+++ b/include/vki/vki-scnums-riscv64-linux.h
@@ -321,6 +321,7 @@
 #define __NR_mmap __NR3264_mmap
 #define __NR_fadvise64 __NR3264_fadvise64
 
+#define __NR_riscv_hwprobe (__NR_arch_specific_syscall + 14)
 #define __NR_riscv_flush_icache (__NR_arch_specific_syscall + 15)
 
 #endif /* __VKI_SCNUMS_RISCV64_LINUX_H */

commit 5efdbbd321e6816ab2ae436d38c20bdcc72b4c17
Author: Mark Wielaard <mark@klomp.org>
Date:   Fri May 9 13:46:44 2025 +0200

    Add workaround for missing riscv_hwprobe syscall (258)
    
    On riscv newer glibc (2.41) will probe instruction support using the
    riscv_hwprobe syscall. Since Valgrind currently doesn't have a wrapper
    for riscv_hwprobe that causes a Warning. Since the RISC-V Hardware
    Probing Interface is non-trivial and we don't really implement
    extended riscv instructions anyway work around that by "implementing"
    riscv_hwprobe as sys_ni_syscall so it generates an ENOSYS and glibc
    will silently fall back to not using any extended instructions.
    
    https://docs.kernel.org/arch/riscv/hwprobe.html
    
    https://bugs.kde.org/show_bug.cgi?id=503253

Just a comment to note that the current "solution" of just pretending that the riscv_hwprobe syscall doesn't exist (return ENOSYS) isn't ideal and prevents use of extended instruction sets.