From 6b3fb29ede140c79a4146fb2056306632e3bd511 Mon Sep 17 00:00:00 2001 From: Andrea Corallo Date: Tue, 19 May 2020 22:33:38 +0100 Subject: [PATCH] ; src/alloc.c: Add a GC reg spill mechanism and Bug#41357 related commentary. --- src/alloc.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-) diff --git a/src/alloc.c b/src/alloc.c index b7ebaa63a5b..d5a6d9167ea 100644 --- a/src/alloc.c +++ b/src/alloc.c @@ -4998,8 +4998,9 @@ mark_stack (char const *bottom, char const *end) #endif } -/* This is a trampoline function that flushes registers to the stack, - and then calls FUNC. ARG is passed through to FUNC verbatim. +/* flush_stack_call_func is the trampoline function that flushes + registers to the stack, and then calls FUNC. ARG is passed through + to FUNC verbatim. This function must be called whenever Emacs is about to release the global interpreter lock. This lets the garbage collector easily @@ -5007,7 +5008,20 @@ mark_stack (char const *bottom, char const *end) Lisp. It is invalid to run any Lisp code or to allocate any GC memory - from FUNC. */ + from FUNC. + + Note: all register spilling is done in flush_stack_call_func before + flush_stack_call_func1 is activated. + + flush_stack_call_func1 is responsible for identifying the stack + address range to be scanned. It *must* be carefully kept as + noinline to make sure that registers has been spilled before it is + called, otherwise given __builtin_frame_address (0) typically + returns the frame pointer (base pointer) and not the stack pointer + [1] GC will miss to scan callee-saved registers content + (Bug#41357). + + [1] . */ NO_INLINE void flush_stack_call_func1 (void (*func) (void *arg), void *arg) -- 2.39.5