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Fix backtraces on cancellation points

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Justine Tunney 2022-11-04 19:55:41 -07:00
parent 022536cab6
commit 0d7c265392
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GPG key ID: BE714B4575D6E328
4 changed files with 22 additions and 13 deletions
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22
libc/sysv/systemfive.S
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@ -108,6 +108,9 @@ __pid: .quad 0
.endobj __pid,globl,hidden
.previous
systemfive_cp:
push %rbp
mov %rsp,%rbp
systemfive_cancellable: # our pthread_cancel() miracle code
cmpb $0,__tls_enabled(%rip) # inspired by the musl libc design!
je 1f # we handle linux and bsd together!
@ -118,12 +121,12 @@ systemfive_cancellable: # our pthread_cancel() miracle code
testb $PT_NOCANCEL,0x00(%r10) # PosixThread::flags
jnz 1f # canceler no cancelling
cmp $0,0x04(%r10) # PosixThread::cancelled
jne _pthread_cancel_sys # tail call for masked mode
.weak _pthread_cancel_sys # must be linked if we're cancelled
jne systemfive_cancel # tail call for masked mode
1: mov %rcx,%r10 # move the fourth argument
clc # no cancellable system calls exist
syscall # that have 7+ args on the bsd OSes
systemfive_cancellable_end: # i/o calls park here for long time
pop %rbp
jc systemfive_errno
jmp 0f
jc 3f # we're now out of the limbo state!
@ -143,10 +146,15 @@ systemfive_cancellable_end: # i/o calls park here for long time
jnz systemfive_errno # cancellation is disabled
cmp $0,0x04(%rcx) # PosixThread::cancelled
je systemfive_errno # we aren't actually cancelled
jmp _pthread_cancel_sys # now we are in fact cancelled
.endfn systemfive_cancellable,globl,hidden
jmp 1f # now we are in fact cancelled
systemfive_cancel:
pop %rbp
1: jmp _pthread_cancel_sys # must be linked if we're cancelled
.weak _pthread_cancel_sys
.globl systemfive_cancellable_end
.hidden systemfive_cancellable_end
.globl systemfive_cancellable
.globl systemfive_cancel
.endfn systemfive_cp
.Lanchorpoint:
#if SupportsLinux() || SupportsMetal()
@ -155,7 +163,7 @@ systemfive_linux:
cmp $0xfff,%eax # checks if unsupported by platform
je systemfive_enosys # never taken branches cost nothing
btr $11,%eax # 0x800 means a call is cancellable
jc systemfive_cancellable # it is handled by the holiest code
jc systemfive_cp # it is handled by the holiest code
mov %rcx,%r10 # syscall instruction clobbers %rcx
push %rbp # linux never reads args from stack
mov %rsp,%rbp # having frame will help backtraces
@ -210,7 +218,7 @@ systemfive_bsd:
cmp $0xfff,%ax
je systemfive_enosys
btr $11,%eax # checks/reset the 800 cancellable bit
jc systemfive_cancellable
jc systemfive_cp
mov %rcx,%r10
syscall # bsd will need arg on stack sometimes
jc systemfive_errno # bsd sets carry flag if %rax is errno