diff options
Diffstat (limited to 'src/pkg')
| -rw-r--r-- | src/pkg/runtime/stack.go | 92 | ||||
| -rw-r--r-- | src/pkg/runtime/stack.h | 4 |
2 files changed, 2 insertions, 94 deletions
diff --git a/src/pkg/runtime/stack.go b/src/pkg/runtime/stack.go index ea27c1fb7..f1b7d32d2 100644 --- a/src/pkg/runtime/stack.go +++ b/src/pkg/runtime/stack.go @@ -4,99 +4,7 @@ package runtime -/* -Stack layout parameters. -Included both by runtime (compiled via 6c) and linkers (compiled via gcc). - -The per-goroutine g->stackguard is set to point stackGuard bytes -above the bottom of the stack. Each function compares its stack -pointer against g->stackguard to check for overflow. To cut one -instruction from the check sequence for functions with tiny frames, -the stack is allowed to protrude stackSmall bytes below the stack -guard. Functions with large frames don't bother with the check and -always call morestack. The sequences are (for amd64, others are -similar): - - guard = g->stackguard - frame = function's stack frame size - argsize = size of function arguments (call + return) - - stack frame size <= stackSmall: - CMPQ guard, SP - JHI 3(PC) - MOVQ m->morearg, $(argsize << 32) - CALL morestack(SB) - - stack frame size > stackSmall but < stackBig - LEAQ (frame-stackSmall)(SP), R0 - CMPQ guard, R0 - JHI 3(PC) - MOVQ m->morearg, $(argsize << 32) - CALL morestack(SB) - - stack frame size >= stackBig: - MOVQ m->morearg, $((argsize << 32) | frame) - CALL morestack(SB) - -The bottom stackGuard - stackSmall bytes are important: there has -to be enough room to execute functions that refuse to check for -stack overflow, either because they need to be adjacent to the -actual caller's frame (deferproc) or because they handle the imminent -stack overflow (morestack). - -For example, deferproc might call malloc, which does one of the -above checks (without allocating a full frame), which might trigger -a call to morestack. This sequence needs to fit in the bottom -section of the stack. On amd64, morestack's frame is 40 bytes, and -deferproc's frame is 56 bytes. That fits well within the -stackGuard - stackSmall = 128 bytes at the bottom. -The linkers explore all possible call traces involving non-splitting -functions to make sure that this limit cannot be violated. -*/ - const ( - // stackSystem is a number of additional bytes to add - // to each stack below the usual guard area for OS-specific - // purposes like signal handling. Used on Windows and on - // Plan 9 because they do not use a separate stack. - // Defined in os_*.go. - - // The amount of extra stack to allocate beyond the size - // needed for the single frame that triggered the split. - stackExtra = 2048 - - // The minimum stack segment size to allocate. - // If the amount needed for the splitting frame + stackExtra - // is less than this number, the stack will have this size instead. - stackMin = 8192 - stackSystemRounded = stackSystem + (-stackSystem & (stackMin - 1)) - Fixedstack = stackMin + stackSystemRounded - - // Functions that need frames bigger than this use an extra - // instruction to do the stack split check, to avoid overflow - // in case SP - framesize wraps below zero. - // This value can be no bigger than the size of the unmapped - // space at zero. - stackBig = 4096 - - // The stack guard is a pointer this many bytes above the - // bottom of the stack. - stackGuard = 256 + stackSystem - - // After a stack split check the SP is allowed to be this - // many bytes below the stack guard. This saves an instruction - // in the checking sequence for tiny frames. - stackSmall = 64 - - // The maximum number of bytes that a chain of NOSPLIT - // functions can use. - stackLimit = stackGuard - stackSystem - stackSmall - - // The assumed size of the top-of-stack data block. - // The actual size can be smaller than this but cannot be larger. - // Checked in proc.c's runtime.malg. - stackTop = 88 - // Goroutine preemption request. // Stored into g->stackguard0 to cause split stack check failure. // Must be greater than any real sp. diff --git a/src/pkg/runtime/stack.h b/src/pkg/runtime/stack.h index dc9da7488..7f8c43ee5 100644 --- a/src/pkg/runtime/stack.h +++ b/src/pkg/runtime/stack.h @@ -89,12 +89,12 @@ enum { // The stack guard is a pointer this many bytes above the // bottom of the stack. - StackGuard = 256 + StackSystem, + StackGuard = 512 + StackSystem, // After a stack split check the SP is allowed to be this // many bytes below the stack guard. This saves an instruction // in the checking sequence for tiny frames. - StackSmall = 64, + StackSmall = 128, // The maximum number of bytes that a chain of NOSPLIT // functions can use. |