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Subject: [PATCH] libgo: use _off_t for mmap offset argument
Date: Thu, 29 Sep 2022 16:49:12 +0200	[thread overview]
Message-ID: <> (raw)

From: Sören Tempel <>

On glibc-based systems, off_t is a 32-bit type on 32-bit systems and a
64-bit type on 64-bit systems by default. However, on systems using musl
libc off_t is unconditionally a 64-bit type. As such, it is insufficient
to use a uintptr type for the mmap offset parameter.

Presently, the (incorrect) mmap declaration causes a libgo run-time
failure on 32-bit musl systems (fatal error: runtime: cannot allocate
memory). This commit fixes this run-time error.

Signed-off-by: Sören Tempel <>
This implements what has been proposed by Ian in a GitHub comment

I don't have access to a 32-bit glibc system to test this on but
this does seem to work fine on 32-bit and 64-bit musl systems.

 libgo/go/runtime/mem_gccgo.go | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/libgo/go/runtime/mem_gccgo.go b/libgo/go/runtime/mem_gccgo.go
index fa3389d8..07bf325a 100644
--- a/libgo/go/runtime/mem_gccgo.go
+++ b/libgo/go/runtime/mem_gccgo.go
@@ -15,7 +15,7 @@ import (
 //go:linkname sysFree
 //extern mmap
-func sysMmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uintptr) unsafe.Pointer
+func sysMmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off _off_t) unsafe.Pointer
 //extern munmap
 func munmap(addr unsafe.Pointer, length uintptr) int32
@@ -38,7 +38,7 @@ func init() {
 func mmap(addr unsafe.Pointer, n uintptr, prot, flags, fd int32, off uintptr) (unsafe.Pointer, int) {
-	p := sysMmap(addr, n, prot, flags, fd, off)
+	p := sysMmap(addr, n, prot, flags, fd, _off_t(off))
 	if uintptr(p) == _MAP_FAILED {
 		return nil, errno()

             reply	other threads:[~2022-09-29 14:49 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-29 14:49 soeren [this message]
2022-10-22 13:45 ` Sören Tempel
2022-10-28  0:13   ` Ian Lance Taylor

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