[uclibc-ng-devel,RFC] Make __syscall_error return long, as expected by syscall() callers
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Message ID 20191019204942.2736-1-unixmania@gmail.com
State New
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  • [uclibc-ng-devel,RFC] Make __syscall_error return long, as expected by syscall() callers
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Commit Message

Carlos Santos Oct. 19, 2019, 8:49 p.m. UTC
From: Carlos Santos <unixmania@gmail.com>

The return type of syscall() is long so __syscall_error, which is jumped
to by syscall handlers to stash an error number into errno, must return
long too otherwhise it returs 4294967295L instead of -1L. For example,
syscall for x86_64 is defined in libc/sysdeps/linux/x86_64/syscall.S as

    syscall:
        movq %rdi, %rax         /* Syscall number -> rax.  */
        movq %rsi, %rdi         /* shift arg1 - arg5.  */
        movq %rdx, %rsi
        movq %rcx, %rdx
        movq %r8, %r10
        movq %r9, %r8
        movq 8(%rsp),%r9        /* arg6 is on the stack.  */
        syscall                 /* Do the system call.  */
        cmpq $-4095, %rax       /* Check %rax for error.  */
        jae __syscall_error     /* Branch forward if it failed.  */
        ret                     /* Return to caller.  */

In libc/sysdeps/linux/x86_64/__syscall_error.c, __syscall_error is
defined as

    int __syscall_error(void) attribute_hidden;
    int __syscall_error(void)
    {
        register int err_no __asm__ ("%rcx");
        __asm__ ("mov %rax, %rcx\n\t"
                 "neg %rcx");
        __set_errno(err_no);
        return -1;
    }

So __syscall_error returns -1 as a 32-bit int in a 64-bit register, %rax
(0x00000000ffffffff, whose decimal value is decimal 4294967295) and a
test like this always returns false:

    if (syscall(number, ...) == -1)
        foo();

Fix the error by making __syscall_error return a long, like syscall().

The problem can be circumvented by the caller by coercing the returned
value to int before comparing it to -1:

    if ((int) syscall(number, ...) == -1)
        foo();

The same problem probably occurs on other 64-bit systems but so far only
x86_64 was tested, so this change must be considered experimental.

Signed-off-by: Carlos Santos <unixmania@gmail.com>
---
 libc/sysdeps/linux/aarch64/__syscall_error.c              | 4 ++--
 libc/sysdeps/linux/alpha/__syscall_error.c                | 2 +-
 libc/sysdeps/linux/arc/__syscall_error.c                  | 2 +-
 libc/sysdeps/linux/arm/__syscall_error.c                  | 4 ++--
 libc/sysdeps/linux/csky/__syscall_error.c                 | 2 +-
 libc/sysdeps/linux/csky/clone.c                           | 2 +-
 libc/sysdeps/linux/frv/sysdep.c                           | 2 +-
 libc/sysdeps/linux/hppa/__syscall_error.c                 | 4 ++--
 libc/sysdeps/linux/i386/__syscall_error.c                 | 4 ++--
 libc/sysdeps/linux/ia64/__syscall_error.c                 | 4 ++--
 libc/sysdeps/linux/m68k/__syscall_error.c                 | 4 ++--
 libc/sysdeps/linux/metag/__syscall_error.c                | 4 ++--
 libc/sysdeps/linux/microblaze/__syscall_error.c           | 4 ++--
 libc/sysdeps/linux/mips/__syscall_error.c                 | 4 ++--
 libc/sysdeps/linux/nds32/__syscall_error.c                | 4 ++--
 libc/sysdeps/linux/nios2/__syscall_error.c                | 4 ++--
 libc/sysdeps/linux/or1k/__syscall_error.c                 | 4 ++--
 libc/sysdeps/linux/powerpc/__syscall_error.c              | 4 ++--
 libc/sysdeps/linux/riscv64/__syscall_error.c              | 4 ++--
 libc/sysdeps/linux/sparc/__syscall_error.c                | 4 ++--
 libc/sysdeps/linux/sparc64/__syscall_error.c              | 4 ++--
 libc/sysdeps/linux/tile/__syscall_error.c                 | 2 +-
 libc/sysdeps/linux/x86_64/__syscall_error.c               | 4 ++--
 libc/sysdeps/linux/xtensa/__syscall_error.c               | 4 ++--
 libpthread/nptl/sysdeps/unix/sysv/linux/__syscall_error.c | 4 ++--
 25 files changed, 44 insertions(+), 44 deletions(-)

Comments

Waldemar Brodkorb Oct. 30, 2019, 10:34 a.m. UTC | #1
Hi Carlos,
unixmania@gmail.com wrote,

> From: Carlos Santos <unixmania@gmail.com>
> 
> The return type of syscall() is long so __syscall_error, which is jumped
> to by syscall handlers to stash an error number into errno, must return
> long too otherwhise it returs 4294967295L instead of -1L. For example,
> syscall for x86_64 is defined in libc/sysdeps/linux/x86_64/syscall.S as
> 
>     syscall:
>         movq %rdi, %rax         /* Syscall number -> rax.  */
>         movq %rsi, %rdi         /* shift arg1 - arg5.  */
>         movq %rdx, %rsi
>         movq %rcx, %rdx
>         movq %r8, %r10
>         movq %r9, %r8
>         movq 8(%rsp),%r9        /* arg6 is on the stack.  */
>         syscall                 /* Do the system call.  */
>         cmpq $-4095, %rax       /* Check %rax for error.  */
>         jae __syscall_error     /* Branch forward if it failed.  */
>         ret                     /* Return to caller.  */
> 
> In libc/sysdeps/linux/x86_64/__syscall_error.c, __syscall_error is
> defined as
> 
>     int __syscall_error(void) attribute_hidden;
>     int __syscall_error(void)
>     {
>         register int err_no __asm__ ("%rcx");
>         __asm__ ("mov %rax, %rcx\n\t"
>                  "neg %rcx");
>         __set_errno(err_no);
>         return -1;
>     }
> 
> So __syscall_error returns -1 as a 32-bit int in a 64-bit register, %rax
> (0x00000000ffffffff, whose decimal value is decimal 4294967295) and a
> test like this always returns false:
> 
>     if (syscall(number, ...) == -1)
>         foo();
> 
> Fix the error by making __syscall_error return a long, like syscall().
> 
> The problem can be circumvented by the caller by coercing the returned
> value to int before comparing it to -1:
> 
>     if ((int) syscall(number, ...) == -1)
>         foo();
> 
> The same problem probably occurs on other 64-bit systems but so far only
> x86_64 was tested, so this change must be considered experimental.

Tested on all supported architectures, no regression in the
testsuite seen.

Thx, applied and pushed,
 Waldemar

Patch
diff mbox series

diff --git a/libc/sysdeps/linux/aarch64/__syscall_error.c b/libc/sysdeps/linux/aarch64/__syscall_error.c
index 2b642e816..c682aae49 100644
--- a/libc/sysdeps/linux/aarch64/__syscall_error.c
+++ b/libc/sysdeps/linux/aarch64/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(-err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/alpha/__syscall_error.c b/libc/sysdeps/linux/alpha/__syscall_error.c
index 7c081f3b5..c986e484d 100644
--- a/libc/sysdeps/linux/alpha/__syscall_error.c
+++ b/libc/sysdeps/linux/alpha/__syscall_error.c
@@ -8,7 +8,7 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
    an error number into errno.  */
-int attribute_hidden __syscall_error (void)
+long attribute_hidden __syscall_error (void)
 {
 	register int err_no __asm__("$0");
 	__set_errno (err_no);
diff --git a/libc/sysdeps/linux/arc/__syscall_error.c b/libc/sysdeps/linux/arc/__syscall_error.c
index 962d743e4..7f30485a8 100644
--- a/libc/sysdeps/linux/arc/__syscall_error.c
+++ b/libc/sysdeps/linux/arc/__syscall_error.c
@@ -8,7 +8,7 @@ 
 #include <errno.h>
 #include <sys/syscall.h>
 
-int __syscall_error(int err_no)
+long __syscall_error(int err_no)
 {
 	__set_errno(-err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/arm/__syscall_error.c b/libc/sysdeps/linux/arm/__syscall_error.c
index 2b642e816..c682aae49 100644
--- a/libc/sysdeps/linux/arm/__syscall_error.c
+++ b/libc/sysdeps/linux/arm/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(-err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/csky/__syscall_error.c b/libc/sysdeps/linux/csky/__syscall_error.c
index cc1fb5977..c6a4a14eb 100644
--- a/libc/sysdeps/linux/csky/__syscall_error.c
+++ b/libc/sysdeps/linux/csky/__syscall_error.c
@@ -8,7 +8,7 @@ 
 #include <errno.h>
 #include <features.h>
 
-int __syscall_error(int err_no)
+long __syscall_error(int err_no)
 {
 	__set_errno(-err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/csky/clone.c b/libc/sysdeps/linux/csky/clone.c
index 991cb8962..f0fcc257b 100644
--- a/libc/sysdeps/linux/csky/clone.c
+++ b/libc/sysdeps/linux/csky/clone.c
@@ -9,7 +9,7 @@ 
 #include <sysdep.h>
 #include <unistd.h>
 
-extern int __syscall_error(int err_no);
+extern long __syscall_error(int err_no);
 
 extern int __csky_clone (
   int flags,
diff --git a/libc/sysdeps/linux/frv/sysdep.c b/libc/sysdeps/linux/frv/sysdep.c
index bfae12100..28beb418f 100644
--- a/libc/sysdeps/linux/frv/sysdep.c
+++ b/libc/sysdeps/linux/frv/sysdep.c
@@ -19,7 +19,7 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
    an error number into errno.  */
-int __syscall_error (int err_no)
+long __syscall_error (int err_no)
 {
   __set_errno (-err_no);
   return -1;
diff --git a/libc/sysdeps/linux/hppa/__syscall_error.c b/libc/sysdeps/linux/hppa/__syscall_error.c
index 5e109a83b..af26cf6ab 100644
--- a/libc/sysdeps/linux/hppa/__syscall_error.c
+++ b/libc/sysdeps/linux/hppa/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/i386/__syscall_error.c b/libc/sysdeps/linux/i386/__syscall_error.c
index 36946bc6d..102ebbedb 100644
--- a/libc/sysdeps/linux/i386/__syscall_error.c
+++ b/libc/sysdeps/linux/i386/__syscall_error.c
@@ -25,8 +25,8 @@ 
 #include <errno.h>
 #include <features.h>
 
-int __syscall_error(void) attribute_hidden;
-int __syscall_error(void)
+long __syscall_error(void) attribute_hidden;
+long __syscall_error(void)
 {
 	register int eax __asm__ ("%eax");
 	int _errno = -eax;
diff --git a/libc/sysdeps/linux/ia64/__syscall_error.c b/libc/sysdeps/linux/ia64/__syscall_error.c
index 0727b2b53..cc2b13450 100644
--- a/libc/sysdeps/linux/ia64/__syscall_error.c
+++ b/libc/sysdeps/linux/ia64/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(void) attribute_hidden;
-int __syscall_error(void)
+long __syscall_error(void) attribute_hidden;
+long __syscall_error(void)
 {
 	register int err_no __asm__("%r8");
 	__set_errno(err_no);
diff --git a/libc/sysdeps/linux/m68k/__syscall_error.c b/libc/sysdeps/linux/m68k/__syscall_error.c
index a29f6ffd6..2d2677521 100644
--- a/libc/sysdeps/linux/m68k/__syscall_error.c
+++ b/libc/sysdeps/linux/m68k/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(void) attribute_hidden;
-int __syscall_error(void)
+long __syscall_error(void) attribute_hidden;
+long __syscall_error(void)
 {
 	register int err_no __asm__("%d0");
 	__set_errno(-err_no);
diff --git a/libc/sysdeps/linux/metag/__syscall_error.c b/libc/sysdeps/linux/metag/__syscall_error.c
index f97cd0126..3e82abe0d 100644
--- a/libc/sysdeps/linux/metag/__syscall_error.c
+++ b/libc/sysdeps/linux/metag/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(-err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/microblaze/__syscall_error.c b/libc/sysdeps/linux/microblaze/__syscall_error.c
index 2b642e816..c682aae49 100644
--- a/libc/sysdeps/linux/microblaze/__syscall_error.c
+++ b/libc/sysdeps/linux/microblaze/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(-err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/mips/__syscall_error.c b/libc/sysdeps/linux/mips/__syscall_error.c
index 5e109a83b..af26cf6ab 100644
--- a/libc/sysdeps/linux/mips/__syscall_error.c
+++ b/libc/sysdeps/linux/mips/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/nds32/__syscall_error.c b/libc/sysdeps/linux/nds32/__syscall_error.c
index 2aa6903e2..c8e6044a7 100644
--- a/libc/sysdeps/linux/nds32/__syscall_error.c
+++ b/libc/sysdeps/linux/nds32/__syscall_error.c
@@ -8,8 +8,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/nios2/__syscall_error.c b/libc/sysdeps/linux/nios2/__syscall_error.c
index 2b642e816..c682aae49 100644
--- a/libc/sysdeps/linux/nios2/__syscall_error.c
+++ b/libc/sysdeps/linux/nios2/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(-err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/or1k/__syscall_error.c b/libc/sysdeps/linux/or1k/__syscall_error.c
index 1b7e8a394..7d1e09d91 100644
--- a/libc/sysdeps/linux/or1k/__syscall_error.c
+++ b/libc/sysdeps/linux/or1k/__syscall_error.c
@@ -17,11 +17,11 @@ 
 
 #include <errno.h>
 
-int __syscall_error (int err_no);
+long __syscall_error (int err_no);
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error (int err_no)
+long __syscall_error (int err_no)
 {
 	__set_errno (err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/powerpc/__syscall_error.c b/libc/sysdeps/linux/powerpc/__syscall_error.c
index 5e109a83b..af26cf6ab 100644
--- a/libc/sysdeps/linux/powerpc/__syscall_error.c
+++ b/libc/sysdeps/linux/powerpc/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/riscv64/__syscall_error.c b/libc/sysdeps/linux/riscv64/__syscall_error.c
index 2b642e816..c682aae49 100644
--- a/libc/sysdeps/linux/riscv64/__syscall_error.c
+++ b/libc/sysdeps/linux/riscv64/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(-err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/sparc/__syscall_error.c b/libc/sysdeps/linux/sparc/__syscall_error.c
index 5e109a83b..af26cf6ab 100644
--- a/libc/sysdeps/linux/sparc/__syscall_error.c
+++ b/libc/sysdeps/linux/sparc/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/sparc64/__syscall_error.c b/libc/sysdeps/linux/sparc64/__syscall_error.c
index 5e109a83b..af26cf6ab 100644
--- a/libc/sysdeps/linux/sparc64/__syscall_error.c
+++ b/libc/sysdeps/linux/sparc64/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/tile/__syscall_error.c b/libc/sysdeps/linux/tile/__syscall_error.c
index a91fdff3a..31cab3799 100644
--- a/libc/sysdeps/linux/tile/__syscall_error.c
+++ b/libc/sysdeps/linux/tile/__syscall_error.c
@@ -6,7 +6,7 @@ 
 #include <errno.h>
 #include <features.h>
 
-int __syscall_error(int err_no)
+long __syscall_error(int err_no)
 {
 	__set_errno(-err_no);
 	return -1;
diff --git a/libc/sysdeps/linux/x86_64/__syscall_error.c b/libc/sysdeps/linux/x86_64/__syscall_error.c
index 448f50983..7f0f388c4 100644
--- a/libc/sysdeps/linux/x86_64/__syscall_error.c
+++ b/libc/sysdeps/linux/x86_64/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(void) attribute_hidden;
-int __syscall_error(void)
+long __syscall_error(void) attribute_hidden;
+long __syscall_error(void)
 {
 	register int err_no __asm__ ("%rcx");
 	__asm__ ("mov %rax, %rcx\n\t"
diff --git a/libc/sysdeps/linux/xtensa/__syscall_error.c b/libc/sysdeps/linux/xtensa/__syscall_error.c
index 2b642e816..c682aae49 100644
--- a/libc/sysdeps/linux/xtensa/__syscall_error.c
+++ b/libc/sysdeps/linux/xtensa/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(-err_no);
 	return -1;
diff --git a/libpthread/nptl/sysdeps/unix/sysv/linux/__syscall_error.c b/libpthread/nptl/sysdeps/unix/sysv/linux/__syscall_error.c
index 5e109a83b..af26cf6ab 100644
--- a/libpthread/nptl/sysdeps/unix/sysv/linux/__syscall_error.c
+++ b/libpthread/nptl/sysdeps/unix/sysv/linux/__syscall_error.c
@@ -10,8 +10,8 @@ 
 
 /* This routine is jumped to by all the syscall handlers, to stash
  * an error number into errno.  */
-int __syscall_error(int err_no) attribute_hidden;
-int __syscall_error(int err_no)
+long __syscall_error(int err_no) attribute_hidden;
+long __syscall_error(int err_no)
 {
 	__set_errno(err_no);
 	return -1;