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| author | Rich Felker <dalias@aerifal.cx> | 2012-10-11 23:09:17 -0400 |
|---|---|---|
| committer | Rich Felker <dalias@aerifal.cx> | 2012-10-11 23:09:17 -0400 |
| commit | 216dca82f6948627f55a0a04ab7d63a12213d8ed (patch) | |
| tree | c197c176c1bb4649024effabce4052bb597a0437 /src | |
| parent | 964e9f3c4c8776820e98c967f3a411d4ca5075a7 (diff) | |
| download | musl-216dca82f6948627f55a0a04ab7d63a12213d8ed.tar.gz | |
comment possibly-confusing i386 vsyscall asm
Diffstat (limited to 'src')
| -rw-r--r-- | src/internal/i386/syscall.s | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/src/internal/i386/syscall.s b/src/internal/i386/syscall.s index 79296ba0..291168c3 100644 --- a/src/internal/i386/syscall.s +++ b/src/internal/i386/syscall.s @@ -1,5 +1,11 @@ .hidden __sysinfo +# The calling convention for __vsyscall has the syscall number +# and 5 args arriving as: eax, edx, ecx, edi, esi, 4(%esp). +# This ensures that the inline asm in the C code never has to touch +# ebx or ebp (which are unavailable in PIC and frame-pointer-using +# code, respectively), and optimizes for size/simplicity in the caller. + .global __vsyscall .type __vsyscall,@function __vsyscall: @@ -22,11 +28,17 @@ __vsyscall: jz 1f push %eax mov 8(%esp),%eax - ret + ret # tail call to kernel vsyscall entry 1: mov 4(%esp),%eax int $128 ret +# The __vsyscall6 entry point is used only for 6-argument syscalls. +# Instead of passing the 5th argument on the stack, a pointer to the +# 5th and 6th arguments is passed. This is ugly, but there are no +# register constraints the inline asm could use that would make it +# possible to pass two arguments on the stack. + .global __vsyscall6 .type __vsyscall6,@function __vsyscall6: |