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all: shrink bdwgc library #4832

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all: shrink bdwgc library #4832

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7 changes: 6 additions & 1 deletion builder/bdwgc.go
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,10 @@ var BoehmGC = Library{
// Use a minimal environment.
"-DNO_MSGBOX_ON_ERROR", // don't call MessageBoxA on Windows
"-DDONT_USE_ATEXIT",
"-DNO_CLOCK", // don't use system clock
"-DNO_DEBUGGING", // reduce code size
"-DGC_NO_FINALIZATION", // finalization is not used at the moment
"-DNO_GETENV", // smaller binary, more predictable configuration
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"-DGC_DISABLE_INCREMENTAL" should also help in decreasing code size

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Also, consider -D SMALL_CONFIG (which implies GC_DISABLE_INCREMENTAL) and -D IGNORE_DYNAMIC_LOADING.

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@aykevl aykevl Mar 29, 2025 •
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I already use -DGC_DISABLE_INCREMENTAL and -DIGNORE_DYNAMIC_LOADING, see a few lines above.
(I might try to enable incremental GC at some point, but I'll need to be careful around handling SIGSEGV etc so it's disabled at the moment. Even with incremental GC disabled, bdwgc is still a lot faster than our own naive GC).

-D SMALL_CONFIG docs say:

Tries to tune the collector for small heap sizes, usually causing it to use less space in such situations. Incremental collection no longer works in this case.

Some people might want to use a large heap size, I'd like to keep that ability. This is a generic configuration, not for a specific program so would like to avoid tuning for a specific configuration.

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You could define -D LARGE_CONFIG in conjunction with -D SMALL_CONFIG. It might seem confllusing a bit:)

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Another available option (with the latest bdwgc master): -D NO_FIND_LEAK


// Special flag to work around the lack of __data_start in ld.lld.
// TODO: try to fix this in LLVM/lld directly so we don't have to
Expand All @@ -38,6 +42,8 @@ var BoehmGC = Library{

// Do not scan the stack. We have our own mechanism to do this.
"-DSTACK_NOT_SCANNED",
"-DNO_PROC_STAT", // we scan the stack manually (don't read /proc/self/stat on Linux)
"-DSTACKBOTTOM=0", // dummy value, we scan the stack manually

// Assertions can be enabled while debugging GC issues.
//"-DGC_ASSERTIONS",
Expand All @@ -59,7 +65,6 @@ var BoehmGC = Library{
"blacklst.c",
"dbg_mlc.c",
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With the latest bdwgc master: dbg_mlc.c is not needed unless you use GC_debug_* API.

"dyn_load.c",
"finalize.c",
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I think there's no need to exclude finalize.c as it should compile to zero size if GC_NO_FINALIZATION is defined.

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Correct, but there's no reason to include it either 🤷

"headers.c",
"mach_dep.c",
"malloc.c",
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