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Message-Id: <20220329115433.918346-2-harald@profian.com>
Date: Tue, 29 Mar 2022 13:54:33 +0200
From: Harald Hoyer <harald@...fian.com>
To: musl@...ts.openwall.com
Cc: Harald Hoyer <harald@...fian.com>
Subject: [PATCH 1/1] feat(x86_64): use wrfsbase if AT_HWCAP2 allows usage
If `AT_HWCAP2` has `HWCAP2_FSGSBASE` set, then instead of calling
`arch_prctl()`, the `wrfsbase` instruction will be used.
This is helpful in SGX contexts, where inside the enclave no other
mechanism is possible.
Tested against `libc-test`.
Signed-off-by: Harald Hoyer <harald@...fian.com>
---
arch/x86_64/bits/hwcap.h | 2 ++
ldso/dynlink.c | 1 +
src/env/__libc_start_main.c | 1 +
src/internal/libc.c | 1 +
src/internal/libc.h | 1 +
src/thread/x86_64/__set_thread_area.c | 14 ++++++++++++++
src/thread/x86_64/__set_thread_area.s | 11 -----------
7 files changed, 20 insertions(+), 11 deletions(-)
create mode 100644 arch/x86_64/bits/hwcap.h
create mode 100644 src/thread/x86_64/__set_thread_area.c
delete mode 100644 src/thread/x86_64/__set_thread_area.s
diff --git a/arch/x86_64/bits/hwcap.h b/arch/x86_64/bits/hwcap.h
new file mode 100644
index 00000000..804d41fa
--- /dev/null
+++ b/arch/x86_64/bits/hwcap.h
@@ -0,0 +1,2 @@
+#define HWCAP2_RING3MWAIT (1 << 0)
+#define HWCAP2_FSGSBASE (1 << 1)
diff --git a/ldso/dynlink.c b/ldso/dynlink.c
index 5b9c8be4..2d38ec63 100644
--- a/ldso/dynlink.c
+++ b/ldso/dynlink.c
@@ -1710,6 +1710,7 @@ void __dls2b(size_t *sp, size_t *auxv)
* use during dynamic linking. If possible it will also serve as the
* thread pointer at runtime. */
search_vec(auxv, &__hwcap, AT_HWCAP);
+ search_vec(auxv, &__hwcap2, AT_HWCAP2);
libc.auxv = auxv;
libc.tls_size = sizeof builtin_tls;
libc.tls_align = tls_align;
diff --git a/src/env/__libc_start_main.c b/src/env/__libc_start_main.c
index c5b277bd..38772bdb 100644
--- a/src/env/__libc_start_main.c
+++ b/src/env/__libc_start_main.c
@@ -28,6 +28,7 @@ void __init_libc(char **envp, char *pn)
libc.auxv = auxv = (void *)(envp+i+1);
for (i=0; auxv[i]; i+=2) if (auxv[i]<AUX_CNT) aux[auxv[i]] = auxv[i+1];
__hwcap = aux[AT_HWCAP];
+ __hwcap2 = aux[AT_HWCAP2];
if (aux[AT_SYSINFO]) __sysinfo = aux[AT_SYSINFO];
libc.page_size = aux[AT_PAGESZ];
diff --git a/src/internal/libc.c b/src/internal/libc.c
index cb051810..16e47633 100644
--- a/src/internal/libc.c
+++ b/src/internal/libc.c
@@ -3,6 +3,7 @@
struct __libc __libc;
size_t __hwcap;
+size_t __hwcap2;
char *__progname=0, *__progname_full=0;
weak_alias(__progname, program_invocation_short_name);
diff --git a/src/internal/libc.h b/src/internal/libc.h
index 619bba86..7d239626 100644
--- a/src/internal/libc.h
+++ b/src/internal/libc.h
@@ -47,6 +47,7 @@ hidden void __libc_exit_fini(void);
hidden void __fork_handler(int);
extern hidden size_t __hwcap;
+extern hidden size_t __hwcap2;
extern hidden size_t __sysinfo;
extern char *__progname, *__progname_full;
diff --git a/src/thread/x86_64/__set_thread_area.c b/src/thread/x86_64/__set_thread_area.c
new file mode 100644
index 00000000..cd3a2519
--- /dev/null
+++ b/src/thread/x86_64/__set_thread_area.c
@@ -0,0 +1,14 @@
+#include <libc.h>
+#include <syscall.h>
+#include <bits/hwcap.h>
+
+hidden int __set_thread_area(void *p)
+{
+ if (__hwcap2 & HWCAP2_FSGSBASE) {
+ __asm__ ("wrfsbase %0" :: "r" (p) : "memory");
+ return 0;
+ }
+
+ // arch_prctl(SET_FS, arg)
+ return syscall(__NR_arch_prctl, 0x1002, p);
+}
diff --git a/src/thread/x86_64/__set_thread_area.s b/src/thread/x86_64/__set_thread_area.s
deleted file mode 100644
index 7347ff4d..00000000
--- a/src/thread/x86_64/__set_thread_area.s
+++ /dev/null
@@ -1,11 +0,0 @@
-/* Copyright 2011-2012 Nicholas J. Kain, licensed under standard MIT license */
-.text
-.global __set_thread_area
-.hidden __set_thread_area
-.type __set_thread_area,@function
-__set_thread_area:
- mov %rdi,%rsi /* shift for syscall */
- movl $0x1002,%edi /* SET_FS register */
- movl $158,%eax /* set fs segment to */
- syscall /* arch_prctl(SET_FS, arg)*/
- ret
--
2.35.1
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