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cmd/link: use uint32 as symbol index

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Currently, a symbol's global index, the Sym type, is defined as an
int, which is 64-bit on 64-bit machines. We're unlikely to have
more than 4 billion symbols in the near future. Even if we will,
we will probably hit some other limit (e.g. section size) before
the symbol number limit. Use a 32-bit type to reduce memory usage.

E,g, linking cmd/compile in external linking mode (on macOS/amd64)

Munmap_GC    43.2M ± 0%     35.5M ± 1%   -17.74%  (p=0.000 n=16+20)

This brings the memory usage back before the previous CL, and even
lower.

Change-Id: Ie185f1586638fe70d8121312bfa9410942d518c7
Reviewed-on: https://go-review.googlesource.com/c/go/+/487416
Reviewed-by: Austin Clements <austin@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>
This commit is contained in:
Cherry Mui 2023-04-21 12:02:30 -04:00
parent 33c06ee12a
commit d33a5136e1
2 changed files with 8 additions and 2 deletions
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2
src/cmd/link/internal/ld/stackcheck.go
View File

@ -42,7 +42,7 @@ const stackCheckCycle int16 = 1<<15 - 1
// stackCheckIndirect is a sentinel Sym value used to represent the // stackCheckIndirect is a sentinel Sym value used to represent the
// target of an indirect/closure call. // target of an indirect/closure call.
const stackCheckIndirect loader.Sym = -1 const stackCheckIndirect loader.Sym = ^loader.Sym(0)
// doStackCheck walks the call tree to check that there is always // doStackCheck walks the call tree to check that there is always
// enough stack space for call frames, especially for a chain of // enough stack space for call frames, especially for a chain of

8
src/cmd/link/internal/loader/loader.go
View File

@ -27,7 +27,7 @@ var _ = fmt.Print
// Sym encapsulates a global symbol index, used to identify a specific // Sym encapsulates a global symbol index, used to identify a specific
// Go symbol. The 0-valued Sym is corresponds to an invalid symbol. // Go symbol. The 0-valued Sym is corresponds to an invalid symbol.
type Sym int type Sym uint32
// Relocs encapsulates the set of relocations on a given symbol; an // Relocs encapsulates the set of relocations on a given symbol; an
// instance of this type is returned by the Loader Relocs() method. // instance of this type is returned by the Loader Relocs() method.
@ -364,6 +364,9 @@ func (st *loadState) addSym(name string, ver int, r *oReader, li uint32, kind in
panic("addSym called after external symbol is created") panic("addSym called after external symbol is created")
} }
i := Sym(len(l.objSyms)) i := Sym(len(l.objSyms))
if int(i) != len(l.objSyms) { // overflow
panic("too many symbols")
}
addToGlobal := func() { addToGlobal := func() {
l.objSyms = append(l.objSyms, objSym{r.objidx, li}) l.objSyms = append(l.objSyms, objSym{r.objidx, li})
} }
@ -485,6 +488,9 @@ func (st *loadState) addSym(name string, ver int, r *oReader, li uint32, kind in
// name/version. // name/version.
func (l *Loader) newExtSym(name string, ver int) Sym { func (l *Loader) newExtSym(name string, ver int) Sym {
i := Sym(len(l.objSyms)) i := Sym(len(l.objSyms))
if int(i) != len(l.objSyms) { // overflow
panic("too many symbols")
}
if l.extStart == 0 { if l.extStart == 0 {
l.extStart = i l.extStart = i
} }