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go/misc/cgo/test/issue9400/asm_386.s

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runtime: run libc SIGSETXID and SIGCANCEL handlers on signal stack These signals are used by glibc to broadcast setuid/setgid to all threads and to send pthread cancellations. Unlike other signals, the Go runtime does not intercept these because they must invoke the libc handlers (see issues #3871 and #6997). However, because 1) these signals may be issued asynchronously by a thread running C code to another thread running Go code and 2) glibc does not set SA_ONSTACK for its handlers, glibc's signal handler may be run on a Go stack. Signal frames range from 1.5K on amd64 to many kilobytes on ppc64, so this may overflow the Go stack and corrupt heap (or other stack) data. Fix this by ensuring that these signal handlers have the SA_ONSTACK flag (but not otherwise taking over the handler). This has been a problem since Go 1.1, but it's likely that people haven't encountered it because it only affects setuid/setgid and pthread_cancel. Fixes #9600. Change-Id: I6cf5f5c2d3aa48998d632f61f1ddc2778dcfd300 Reviewed-on: https://go-review.googlesource.com/1887 Reviewed-by: Ian Lance Taylor <iant@golang.org>
2014-12-19 14:16:17 -07:00
#include "textflag.h"
TEXT ·RewindAndSetgid(SB),NOSPLIT,$0-0
// Rewind stack pointer so anything that happens on the stack
// will clobber the test pattern created by the caller
ADDL $(1024 * 8), SP
// Ask signaller to setgid
MOVL $1, ·Baton(SB)
// Wait for setgid completion
loop:
PAUSE
MOVL ·Baton(SB), AX
CMPL AX, $0
JNE loop
// Restore stack
SUBL $(1024 * 8), SP
RET
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