The branch main has been updated by emaste: URL: https://cgit.FreeBSD.org/src/commit/?id=89d7b30c652c98ea12abc5eb9424464cbfb45953
commit 89d7b30c652c98ea12abc5eb9424464cbfb45953 Author: Aaron LI <[email protected]> AuthorDate: 2026-02-16 04:00:12 +0000 Commit: Ed Maste <[email protected]> CommitDate: 2026-02-20 15:26:20 +0000 i386,amd64: Explicitly set ECX=0 in do_cpuid() to be future-proof In principle, do_cpuid() should only be used for CPUID leaves without sub-leaves. Even accessing sub-leaf zero (ECX=0), one must use cpuid_count(ax, 0) rather than cpuid(ax). However, one might assume do_cpuid(ax) is equivalent to cpuid_count(ax, 0), but the old do_cpuid() did not initialize ECX before executing the CPUID instruction. If ECX contained a non-zero value, the instruction could return unexpected results, potentially leading to subtle and hard-to-debug issues, especially in ported code. To be future-proof and to help port code, adjust do_cpuid(ax) to be cpuid_count(ax, 0) to explicitly set ECX=0. It's believed that this change does not fix any real bugs in FreeBSD. See also the DragonFly commit: https://github.com/DragonFlyBSD/DragonFlyBSD/commit/0087a1d163488a57787a9a6431dd94070b1988d4 Signed-off-by: Aaron LI <[email protected]> Reviewed by: kib Pull Request: https://github.com/freebsd/freebsd-src/pull/2027 --- sys/amd64/include/cpufunc.h | 10 ++++------ sys/i386/include/cpufunc.h | 24 +++++------------------- 2 files changed, 9 insertions(+), 25 deletions(-) diff --git a/sys/amd64/include/cpufunc.h b/sys/amd64/include/cpufunc.h index 9a4c82275a99..e52c55dc80f0 100644 --- a/sys/amd64/include/cpufunc.h +++ b/sys/amd64/include/cpufunc.h @@ -100,19 +100,17 @@ disable_intr(void) } static __inline void -do_cpuid(u_int ax, u_int *p) +cpuid_count(u_int ax, u_int cx, u_int *p) { __asm __volatile("cpuid" : "=a" (p[0]), "=b" (p[1]), "=c" (p[2]), "=d" (p[3]) - : "0" (ax)); + : "0" (ax), "c" (cx)); } static __inline void -cpuid_count(u_int ax, u_int cx, u_int *p) +do_cpuid(u_int ax, u_int *p) { - __asm __volatile("cpuid" - : "=a" (p[0]), "=b" (p[1]), "=c" (p[2]), "=d" (p[3]) - : "0" (ax), "c" (cx)); + cpuid_count(ax, 0, p); } static __inline void diff --git a/sys/i386/include/cpufunc.h b/sys/i386/include/cpufunc.h index b200588b0739..5ee516656d72 100644 --- a/sys/i386/include/cpufunc.h +++ b/sys/i386/include/cpufunc.h @@ -91,14 +91,6 @@ disable_intr(void) } #ifdef _KERNEL -static __inline void -do_cpuid(u_int ax, u_int *p) -{ - __asm __volatile("cpuid" - : "=a" (p[0]), "=b" (p[1]), "=c" (p[2]), "=d" (p[3]) - : "0" (ax)); -} - static __inline void cpuid_count(u_int ax, u_int cx, u_int *p) { @@ -108,7 +100,7 @@ cpuid_count(u_int ax, u_int cx, u_int *p) } #else static __inline void -do_cpuid(u_int ax, u_int *p) +cpuid_count(u_int ax, u_int cx, u_int *p) { __asm __volatile( "pushl\t%%ebx\n\t" @@ -116,21 +108,15 @@ do_cpuid(u_int ax, u_int *p) "movl\t%%ebx,%1\n\t" "popl\t%%ebx" : "=a" (p[0]), "=DS" (p[1]), "=c" (p[2]), "=d" (p[3]) - : "0" (ax)); + : "0" (ax), "c" (cx)); } +#endif static __inline void -cpuid_count(u_int ax, u_int cx, u_int *p) +do_cpuid(u_int ax, u_int *p) { - __asm __volatile( - "pushl\t%%ebx\n\t" - "cpuid\n\t" - "movl\t%%ebx,%1\n\t" - "popl\t%%ebx" - : "=a" (p[0]), "=DS" (p[1]), "=c" (p[2]), "=d" (p[3]) - : "0" (ax), "c" (cx)); + cpuid_count(ax, 0, p); } -#endif static __inline void enable_intr(void)
