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

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>

1 files changed, 1 insertions, 1 deletions

diff --git a/src/cmd/link/internal/arm/asm.go b/src/cmd/link/internal/arm/asm.go
index 1e4b36df48..4574f2d5f9 100644
--- 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.