cmd/link/internal/arm: fix off-by-1 in trampoline reachability computation

thanm · thanm · commit f26bf203ac67 · 2023-03-15T17:32:28.000Z
Tweak the code in trampoline generation that determines if a given call branch will reach, changing the lower limit guard from "x < -0x800000" to "x <= -0x800000". This is to resolve linking failures when the computed displacement is exactly -0x800000, which results in errors of the form .../ld.gold: internal error in arm_branch_common, at ../../gold/arm.cc:4079 when using the Gold linker, and ...:(.text+0x...): relocation truncated to fit: R_ARM_CALL against `runtime.morestack_noctxt' when using the bfd linker. Fixes #59034. Updates #58425. Change-Id: I8a76986b38727df1b961654824c2af23f06b9fcf Reviewed-on: https://go-review.googlesource.com/c/go/+/475957 Run-TryBot: Than McIntosh <thanm@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Cherry Mui <cherryyz@google.com>
diff --git a/src/cmd/link/internal/arm/asm.go b/src/cmd/link/internal/arm/asm.go
@@ -417,7 +417,7 @@ func trampoline(ctxt *ld.Link, ldr *loader.Loader, ri int, rs, s loader.Sym) {
 				t = (ldr.SymValue(rs) + int64(signext24(r.Add()&0xffffff)*4) - (ldr.SymValue(s) + int64(r.Off()))) / 4
 			}
 		}
-		if t > 0x7fffff || t < -0x800000 || ldr.SymValue(rs) == 0 || (*ld.FlagDebugTramp > 1 && ldr.SymPkg(s) != ldr.SymPkg(rs)) {
+		if t > 0x7fffff || t <= -0x800000 || ldr.SymValue(rs) == 0 || (*ld.FlagDebugTramp > 1 && ldr.SymPkg(s) != ldr.SymPkg(rs)) {
 			// direct call too far, need to insert trampoline.
 			// look up existing trampolines first. if we found one within the range
 			// of direct call, we can reuse it. otherwise create a new one.

Original file line number	Diff line number	Diff line change
`@@ -417,7 +417,7 @@ func trampoline(ctxt ld.Link, ldr loader.Loader, ri int, rs, s loader.Sym) {`
`417`	`417`	`t = (ldr.SymValue(rs) + int64(signext24(r.Add()&0xffffff)*4) - (ldr.SymValue(s) + int64(r.Off()))) / 4`
`418`	`418`	`}`
`419`	`419`	`}`
`420`		`- if t > 0x7fffff \|\| t < -0x800000 \|\| ldr.SymValue(rs) == 0 \|\| (*ld.FlagDebugTramp > 1 && ldr.SymPkg(s) != ldr.SymPkg(rs)) {`
	`420`	`+ if t > 0x7fffff \|\| t <= -0x800000 \|\| ldr.SymValue(rs) == 0 \|\| (*ld.FlagDebugTramp > 1 && ldr.SymPkg(s) != ldr.SymPkg(rs)) {`
`421`	`421`	`// direct call too far, need to insert trampoline.`
`422`	`422`	`// look up existing trampolines first. if we found one within the range`
`423`	`423`	`// of direct call, we can reuse it. otherwise create a new one.`