[PATCH] gas: Fix checking for backwards .org with negative offset

[PATCH] gas: Fix checking for backwards .org with negative offset

[Alex Coplan]

[-- Attachment #1: Type: text/plain, Size: 1934 bytes --]

Hello,

This patch fixes internal errors in (at least) arm and aarch64 GAS when
assembling code that attempts a negative .org. For example, assembling:

.=-1
nop

would give:

test.s: Assembler messages:
test.s:1: Error: attempt to .org/.space/.nops backwards? (-1)
test.s: Internal error in check_mapping_symbols at ../../../binutils-gdb/gas/config/tc-aarch64.c:8557.
Please report this bug.

on aarch64, and:

test.s: Assembler messages:
test.s:1: Error: attempt to .org/.space/.nops backwards? (-1)
test.s: Internal error in make_mapping_symbol at ../../../../src/binutils-gdb/gas/config/tc-arm.c:3017.
Please report this bug.

on arm.

The bug appears to be a regression introduced in binutils-2.29 by this
commit:
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=9875b36538d35f2292ddc3bb5e7c60e1582aa087

The problem is in the rs_org case of the main switch statement in
gas/write.c:relax_segment(). This code assigns the signed variable
`offset' to the unsigned variable `target' and then proceeds to do an
unsigned comparison:

  if (address + fragP->fr_fix > target)

which fails in this case because `offset' was -1 and so `target' wrapped
to become UINT64_MAX.

This patch uses a signed type for `target' and casts the LHS to ensure a
signed comparison is used here.

Testing:
 * New tests for arm and aarch64.
 * Regression tested on a wide variety of targets.
 * Bootstrapped on aarch64.

Ok for master and backport to binutils-2.34?

Thanks,
Alex

---

gas/ChangeLog:

2020-05-29  Alex Coplan  <alex.coplan@arm.com>

	* testsuite/gas/aarch64/org-neg.d: New test.
	* testsuite/gas/aarch64/org-neg.l: Error output for test.
	* testsuite/gas/aarch64/org-neg.s: Input for test.
	* testsuite/gas/arm/org-neg.d: New test.
	* testsuite/gas/arm/org-neg.l: Error output for test.
	* testsuite/gas/arm/org-neg.s: Input for test.
	* write.c (relax_segment): Fix handling of negative offset when
	  relaxing an rs_org frag.

[-- Attachment #2: patch.txt --]
[-- Type: text/plain, Size: 2281 bytes --]

diff --git a/gas/testsuite/gas/aarch64/org-neg.d b/gas/testsuite/gas/aarch64/org-neg.d
new file mode 100644
index 0000000000..83e6af6afb
--- /dev/null
+++ b/gas/testsuite/gas/aarch64/org-neg.d
@@ -0,0 +1,3 @@
+#name: negative org should not cause internal error
+#source: org-neg.s
+#error_output: org-neg.l
diff --git a/gas/testsuite/gas/aarch64/org-neg.l b/gas/testsuite/gas/aarch64/org-neg.l
new file mode 100644
index 0000000000..f8414adc19
--- /dev/null
+++ b/gas/testsuite/gas/aarch64/org-neg.l
@@ -0,0 +1,2 @@
+[^:]*: Assembler messages:
+.*: Error: attempt to move .org backwards
diff --git a/gas/testsuite/gas/aarch64/org-neg.s b/gas/testsuite/gas/aarch64/org-neg.s
new file mode 100644
index 0000000000..403e70d5e0
--- /dev/null
+++ b/gas/testsuite/gas/aarch64/org-neg.s
@@ -0,0 +1,2 @@
+.=-1
+ret
diff --git a/gas/testsuite/gas/arm/org-neg.d b/gas/testsuite/gas/arm/org-neg.d
new file mode 100644
index 0000000000..83e6af6afb
--- /dev/null
+++ b/gas/testsuite/gas/arm/org-neg.d
@@ -0,0 +1,3 @@
+#name: negative org should not cause internal error
+#source: org-neg.s
+#error_output: org-neg.l
diff --git a/gas/testsuite/gas/arm/org-neg.l b/gas/testsuite/gas/arm/org-neg.l
new file mode 100644
index 0000000000..f8414adc19
--- /dev/null
+++ b/gas/testsuite/gas/arm/org-neg.l
@@ -0,0 +1,2 @@
+[^:]*: Assembler messages:
+.*: Error: attempt to move .org backwards
diff --git a/gas/testsuite/gas/arm/org-neg.s b/gas/testsuite/gas/arm/org-neg.s
new file mode 100644
index 0000000000..f60486e2c8
--- /dev/null
+++ b/gas/testsuite/gas/arm/org-neg.s
@@ -0,0 +1,2 @@
+.=-1
+nop
diff --git a/gas/write.c b/gas/write.c
index 5825117548..398c50bec0 100644
--- a/gas/write.c
+++ b/gas/write.c
@@ -2940,7 +2940,7 @@ relax_segment (struct frag *segment_frag_root, segT segment, int pass)
 
 	      case rs_org:
 		{
-		  addressT target = offset;
+		  offsetT target = offset;
 		  addressT after;
 
 		  if (symbolP)
@@ -2960,7 +2960,7 @@ relax_segment (struct frag *segment_frag_root, segT segment, int pass)
 		  /* Growth may be negative, but variable part of frag
 		     cannot have fewer than 0 chars.  That is, we can't
 		     .org backwards.  */
-		  if (address + fragP->fr_fix > target)
+		  if ((offsetT)(address + fragP->fr_fix) > target)
 		    {
 		      growth = 0;
 

Re: [PATCH] gas: Fix checking for backwards .org with negative offset

[Alan Modra]

On Fri, May 29, 2020 at 04:04:50PM +0100, Alex Coplan wrote:
> 	* testsuite/gas/aarch64/org-neg.d: New test.
> 	* testsuite/gas/aarch64/org-neg.l: Error output for test.
> 	* testsuite/gas/aarch64/org-neg.s: Input for test.
> 	* testsuite/gas/arm/org-neg.d: New test.
> 	* testsuite/gas/arm/org-neg.l: Error output for test.
> 	* testsuite/gas/arm/org-neg.s: Input for test.
> 	* write.c (relax_segment): Fix handling of negative offset when
> 	  relaxing an rs_org frag.

This is OK everywhere with the formatting fixed.

> -		  if (address + fragP->fr_fix > target)
> +		  if ((offsetT)(address + fragP->fr_fix) > target)

		  if ((offsetT) (address + fragP->fr_fix) > target)

-- 
Alan Modra
Australia Development Lab, IBM

RE: [PATCH] gas: Fix checking for backwards .org with negative offset

[Alex Coplan]

> -----Original Message-----
> From: Alan Modra <amodra@gmail.com>
> Sent: 31 May 2020 23:52
> To: Alex Coplan <Alex.Coplan@arm.com>
> Cc: binutils@sourceware.org; Ramana Radhakrishnan
> <Ramana.Radhakrishnan@arm.com>; nd <nd@arm.com>; Richard Earnshaw
> <Richard.Earnshaw@arm.com>; Marcus Shawcroft <Marcus.Shawcroft@arm.com>
> Subject: Re: [PATCH] gas: Fix checking for backwards .org with negative
> offset
> 
> On Fri, May 29, 2020 at 04:04:50PM +0100, Alex Coplan wrote:
> > 	* testsuite/gas/aarch64/org-neg.d: New test.
> > 	* testsuite/gas/aarch64/org-neg.l: Error output for test.
> > 	* testsuite/gas/aarch64/org-neg.s: Input for test.
> > 	* testsuite/gas/arm/org-neg.d: New test.
> > 	* testsuite/gas/arm/org-neg.l: Error output for test.
> > 	* testsuite/gas/arm/org-neg.s: Input for test.
> > 	* write.c (relax_segment): Fix handling of negative offset when
> > 	  relaxing an rs_org frag.
> 
> This is OK everywhere with the formatting fixed.
> 
> > -		  if (address + fragP->fr_fix > target)
> > +		  if ((offsetT)(address + fragP->fr_fix) > target)
> 
> 		  if ((offsetT) (address + fragP->fr_fix) > target)
> 

Hi Alan,

Thanks. I should have mentioned in my original email that I don't have
commit access so I'll need a maintainer to commit on my behalf.

Alex

RE: [PATCH] gas: Fix checking for backwards .org with negative offset

[Alex Coplan]

> -----Original Message-----
> From: Alex Coplan
> Sent: 01 June 2020 09:07
> To: Alan Modra <amodra@gmail.com>
> Cc: binutils@sourceware.org; Ramana Radhakrishnan
> <Ramana.Radhakrishnan@arm.com>; nd <nd@arm.com>; Richard Earnshaw
> <Richard.Earnshaw@arm.com>; Marcus Shawcroft <Marcus.Shawcroft@arm.com>
> Subject: RE: [PATCH] gas: Fix checking for backwards .org with negative
> offset
> 
> > -----Original Message-----
> > From: Alan Modra <amodra@gmail.com>
> > Sent: 31 May 2020 23:52
> > To: Alex Coplan <Alex.Coplan@arm.com>
> > Cc: binutils@sourceware.org; Ramana Radhakrishnan
> > <Ramana.Radhakrishnan@arm.com>; nd <nd@arm.com>; Richard Earnshaw
> > <Richard.Earnshaw@arm.com>; Marcus Shawcroft <Marcus.Shawcroft@arm.com>
> > Subject: Re: [PATCH] gas: Fix checking for backwards .org with negative
> > offset
> >
> > On Fri, May 29, 2020 at 04:04:50PM +0100, Alex Coplan wrote:
> > > 	* testsuite/gas/aarch64/org-neg.d: New test.
> > > 	* testsuite/gas/aarch64/org-neg.l: Error output for test.
> > > 	* testsuite/gas/aarch64/org-neg.s: Input for test.
> > > 	* testsuite/gas/arm/org-neg.d: New test.
> > > 	* testsuite/gas/arm/org-neg.l: Error output for test.
> > > 	* testsuite/gas/arm/org-neg.s: Input for test.
> > > 	* write.c (relax_segment): Fix handling of negative offset when
> > > 	  relaxing an rs_org frag.
> >
> > This is OK everywhere with the formatting fixed.
> >
> > > -		  if (address + fragP->fr_fix > target)
> > > +		  if ((offsetT)(address + fragP->fr_fix) > target)
> >
> > 		  if ((offsetT) (address + fragP->fr_fix) > target)
> >
> 
> Hi Alan,
> 
> Thanks. I should have mentioned in my original email that I don't have
> commit access so I'll need a maintainer to commit on my behalf.
> 
> Alex

Does this also need backporting to binutils-2.34? If so, I'll need a
maintainer to do it on my behalf.

Thanks,
Alex

Re: [PATCH] gas: Fix checking for backwards .org with negative offset

[Alan Modra]

On Tue, Jun 09, 2020 at 02:06:41PM +0000, Alex Coplan wrote:
> Does this also need backporting to binutils-2.34? If so, I'll need a
> maintainer to do it on my behalf.

Yes, I think patch could be safely backported.  I'll commit it after
running regression tests on the 2.34 branch.

-- 
Alan Modra
Australia Development Lab, IBM