[PATCH] mips: align stack in clone [BZ #28223]

[PATCH] mips: align stack in clone [BZ #28223]

[Xi Ruoyao]

The MIPS O32 ABI requires 4 byte aligned stack, and the MIPS N64 and N32
ABI require 8 byte aligned stack.  Previously if the caller passed an
unaligned stack to clone the the child misbehaved.

Fixes bug 28223.
---
 sysdeps/unix/sysv/linux/mips/clone.S | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/mips/clone.S b/sysdeps/unix/sysv/linux/mips/clone.S
index 71d9dba8bd..9e5826aeba 100644
--- a/sysdeps/unix/sysv/linux/mips/clone.S
+++ b/sysdeps/unix/sysv/linux/mips/clone.S
@@ -55,6 +55,13 @@ NESTED(__clone,4*SZREG,sp)
 	.set		at
 #endif
 
+        /* Align stack to 4/8 bytes per the ABI */
+#if _MIPS_SIM == _ABIO32
+	li		t0,-4
+#else
+	li		t0,-8
+#endif
+	and		a1,a1,t0
 
 	/* Sanity check arguments.  */
 	li		v0,EINVAL
-- 
2.32.0

Re: [PATCH] mips: align stack in clone [BZ #28223]

[Joseph Myers]

On Fri, 13 Aug 2021, Xi Ruoyao via Libc-alpha wrote:

> The MIPS O32 ABI requires 4 byte aligned stack, and the MIPS N64 and N32
> ABI require 8 byte aligned stack.  Previously if the caller passed an
> unaligned stack to clone the the child misbehaved.
> 
> Fixes bug 28223.

This patch is OK.

-- 
Joseph S. Myers
joseph@codesourcery.com

Re: [PATCH] mips: align stack in clone [BZ #28223]

[Xi Ruoyao]

On Thu, 2021-08-12 at 17:20 +0000, Joseph Myers wrote:
> On Fri, 13 Aug 2021, Xi Ruoyao via Libc-alpha wrote:
> 
> > The MIPS O32 ABI requires 4 byte aligned stack, and the MIPS N64 and
> > N32
> > ABI require 8 byte aligned stack.  Previously if the caller passed
> > an
> > unaligned stack to clone the the child misbehaved.
> > 
> > Fixes bug 28223.
> 
> This patch is OK.
> 

I don't have git write access, waiting for a maintainer to push it.

Re: [PATCH] mips: align stack in clone [BZ #28223]

[Joseph Myers]

On Fri, 13 Aug 2021, Xi Ruoyao via Libc-alpha wrote:

> On Thu, 2021-08-12 at 17:20 +0000, Joseph Myers wrote:
> > On Fri, 13 Aug 2021, Xi Ruoyao via Libc-alpha wrote:
> > 
> > > The MIPS O32 ABI requires 4 byte aligned stack, and the MIPS N64 and
> > > N32
> > > ABI require 8 byte aligned stack.  Previously if the caller passed
> > > an
> > > unaligned stack to clone the the child misbehaved.
> > > 
> > > Fixes bug 28223.
> > 
> > This patch is OK.
> 
> I don't have git write access, waiting for a maintainer to push it.

Now pushed.

-- 
Joseph S. Myers
joseph@codesourcery.com

[PATCH] mips: increase stack alignment in clone to match the ABI

[Xi Ruoyao]

Hi Joseph,

Sorry for this, but I have to admit I've made an error in the previous
patch.  In MIPS documentations one "word" is defined 32-bit (4-byte), so
a "doubleword" is 8-byte and a "quadword" is 16-byte.  I misinterpreted
"doubleword" as a "dword" we normally uses for 4-byte, so the alignment
is actually insufficient.

I'm not sure why "tst-misaligned-stack" passed with the previous
problematic patch on my board.  Maybe it was pure luck, or my CPU used
to test the patch supports some non-standard unaligned access.

The following patch should fix this:

In "mips: align stack in clone [BZ #28223]"
(commit 1f51cd9a860ee45eee8a56fb2ba925267a2a7bfe) I made a mistake: I
misbelieved one "word" was 2-byte and "doubleword" should be 4-byte.
But in MIPS ABI one "word" is defined 32-bit (4-byte), so "doubleword" is
8-byte [1], and "quadword" is 16-byte [2].

[1]: "System V Application Binary Interface: MIPS(R) RISC Processor
      Supplement, 3rd edition", page 3-31
[2]: "MIPSpro(TM) 64-Bit Porting and Transition Guide", page 23
---
 sysdeps/unix/sysv/linux/mips/clone.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/mips/clone.S b/sysdeps/unix/sysv/linux/mips/clone.S
index 43a5ad3a40..81d814ba4d 100644
--- a/sysdeps/unix/sysv/linux/mips/clone.S
+++ b/sysdeps/unix/sysv/linux/mips/clone.S
@@ -57,9 +57,9 @@ NESTED(__clone,4*SZREG,sp)
 
 	/* Align stack to 4/8 bytes per the ABI.  */
 #if _MIPS_SIM == _ABIO32
-	li		t0,-4
-#else
 	li		t0,-8
+#else
+	li		t0,-16
 #endif
 	and		a1,a1,t0
 
-- 
2.32.0

Sorry again for the error.

[PATCH v2] mips: increase stack alignment in clone to match the ABI

[Xi Ruoyao]

v2: change the comment along with the code

I must have been too sleepy in recent two days...

--
In "mips: align stack in clone [BZ #28223]"
(commit 1f51cd9a860ee45eee8a56fb2ba925267a2a7bfe) I made a mistake: I
misbelieved one "word" was 2-byte and "doubleword" should be 4-byte.
But in MIPS ABI one "word" is defined 32-bit (4-byte), so "doubleword" is
8-byte [1], and "quadword" is 16-byte [2].

[1]: "System V Application Binary Interface: MIPS(R) RISC Processor
      Supplement, 3rd edition", page 3-31
[2]: "MIPSpro(TM) 64-Bit Porting and Transition Guide", page 23
---
 sysdeps/unix/sysv/linux/mips/clone.S | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/sysdeps/unix/sysv/linux/mips/clone.S b/sysdeps/unix/sysv/linux/mips/clone.S
index 43a5ad3a40..fd71b5ca2e 100644
--- a/sysdeps/unix/sysv/linux/mips/clone.S
+++ b/sysdeps/unix/sysv/linux/mips/clone.S
@@ -55,11 +55,11 @@ NESTED(__clone,4*SZREG,sp)
 	.set		at
 #endif
 
-	/* Align stack to 4/8 bytes per the ABI.  */
+	/* Align stack to 8/16 bytes per the ABI.  */
 #if _MIPS_SIM == _ABIO32
-	li		t0,-4
-#else
 	li		t0,-8
+#else
+	li		t0,-16
 #endif
 	and		a1,a1,t0
 
-- 
2.32.0



On Fri, 2021-08-13 at 18:43 +0800, Xi Ruoyao wrote:
> Hi Joseph,
> 
> Sorry for this, but I have to admit I've made an error in the previous
> patch.  In MIPS documentations one "word" is defined 32-bit (4-byte), so
> a "doubleword" is 8-byte and a "quadword" is 16-byte.  I misinterpreted
> "doubleword" as a "dword" we normally uses for 4-byte, so the alignment
> is actually insufficient.

Re: [PATCH v2] mips: increase stack alignment in clone to match the ABI

[Joseph Myers]

Thanks, I've applied this followup fix as well.

-- 
Joseph S. Myers
joseph@codesourcery.com