diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/pkg/runtime/sys_freebsd_amd64.s | 25 | ||||
| -rw-r--r-- | src/pkg/syscall/asm_freebsd_amd64.s | 5 |
2 files changed, 30 insertions, 0 deletions
diff --git a/src/pkg/runtime/sys_freebsd_amd64.s b/src/pkg/runtime/sys_freebsd_amd64.s index e4aa7aabd..ef3beaedc 100644 --- a/src/pkg/runtime/sys_freebsd_amd64.s +++ b/src/pkg/runtime/sys_freebsd_amd64.s @@ -8,6 +8,31 @@ #include "zasm_GOOS_GOARCH.h" #include "../../cmd/ld/textflag.h" + +// FreeBSD 8, FreeBSD 9, and older versions that I have checked +// do not restore R10 on exit from a "restarted" system call +// if you use the SYSCALL instruction. This means that, for example, +// if a signal arrives while the wait4 system call is executing, +// the wait4 internally returns ERESTART, which makes the kernel +// back up the PC to execute the SYSCALL instruction a second time. +// However, since the kernel does not restore R10, the fourth +// argument to the system call has been lost. (FreeBSD 9 also fails +// to restore the fifth and sixth arguments, R8 and R9, although +// some earlier versions did restore those correctly.) +// The broken code is in fast_syscall in FreeBSD's amd64/amd64/exception.S. +// It restores only DI, SI, DX, AX, and RFLAGS on system call return. +// http://fxr.watson.org/fxr/source/amd64/amd64/exception.S?v=FREEBSD91#L399 +// +// The INT $0x80 system call path (int0x80_syscall in FreeBSD's +// amd64/ia32/ia32_exception.S) does not have this problem, +// but it expects the third argument in R10. Instead of rewriting +// all the assembly in this file, #define SYSCALL to a safe simulation +// using INT $0x80. +/ +// INT $0x80 is a little slower than SYSCALL, but correctness wins. +// +// See golang.org/issue/6372. +#define SYSCALL MOVQ R10, CX; INT $0x80 TEXT runtime·sys_umtx_op(SB),NOSPLIT,$0 MOVQ 8(SP), DI diff --git a/src/pkg/syscall/asm_freebsd_amd64.s b/src/pkg/syscall/asm_freebsd_amd64.s index 72279d0af..fca7f371e 100644 --- a/src/pkg/syscall/asm_freebsd_amd64.s +++ b/src/pkg/syscall/asm_freebsd_amd64.s @@ -8,6 +8,11 @@ // System call support for AMD64, FreeBSD // +// The SYSCALL variant for invoking system calls is broken in FreeBSD. +// See comment at top of ../runtime/sys_freebsd_amd64.c and +// golang.org/issue/6372. +#define SYSCALL MOVQ R10, CX; INT $0x80 + // func Syscall(trap int64, a1, a2, a3 int64) (r1, r2, err int64); // func Syscall6(trap int64, a1, a2, a3, a4, a5, a6 int64) (r1, r2, err int64); // func Syscall9(trap int64, a1, a2, a3, a4, a5, a6, a7, a8, a9 int64) (r1, r2, err int64) |