[Bug lto/65991] New: maybe-unitialized - false positive

[Bug lto/65991] New: maybe-unitialized - false positive

[dilyan.palauzov at aegee dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65991

            Bug ID: 65991
           Summary: maybe-unitialized - false positive
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dilyan.palauzov at aegee dot org
  Target Milestone: ---

I have compiled gcc with

../gcc-4.9.2/configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var
--enable-threads=posix --enable-nls --enable-interpreter --with-system-zlib
--enable-libgcj-multifile --enable-languages=all --enable-targets=all
--with-system-unwind --without-x --with-linker-hash-style=gnu --enable-multilib
--disable-multilib --with-arch=nocona

export CFLAGS="-pipe -O3 -fno-fat-lto-objects -flto"
export CXXFLAGS="-pipe -O3 -fno-fat-lto-objects -flto"


Then I try to compile binutils (at commit 01a97082d0e9) with

configure --enable-lto --enable-plugins --enable-threads --enable-gold=yes
--with-zlib
CFLAGS='-pipe -O3 -fno-fat-lto-objects -flto'
LDFLAGS='-Wl,-O1 -Wl,-z,relro -Wl,-s'

bintuils utilizies internally -Werror and compiling it fails with LTO error at:

make[2]: Entering directory '/mnt/new/src/gcc/binutil-git/gas'
/bin/sh ./libtool --tag=CC   --mode=link gcc -W -Wall -Wstrict-prototypes
-Wmissing-prototypes -Wshadow -Werror -I/home/git/binutils-gdb/gas/../zlib
-pipe -O3 -fno-fat-lto-objects -flto  -Wl,-O1 -Wl,-z,relro -Wl,-s -o as-new
app.o as.o atof-generic.o compress-debug.o cond.o depend.o dwarf2dbg.o
dw2gencfi.o ecoff.o ehopt.o expr.o flonum-copy.o flonum-konst.o flonum-mult.o
frags.o hash.o input-file.o input-scrub.o listing.o literal.o macro.o
messages.o output-file.o read.o remap.o sb.o stabs.o subsegs.o symbols.o
write.o tc-i386.o obj-elf.o atof-ieee.o  ../opcodes/libopcodes.la
../bfd/libbfd.la ../libiberty/libiberty.a   -ldl 
libtool: link: gcc -W -Wall -Wstrict-prototypes -Wmissing-prototypes -Wshadow
-Werror -I/home/git/binutils-gdb/gas/../zlib -pipe -O3 -fno-fat-lto-objects
-flto -Wl,-O1 -Wl,-z -Wl,relro -Wl,-s -o as-new app.o as.o atof-generic.o
compress-debug.o cond.o depend.o dwarf2dbg.o dw2gencfi.o ecoff.o ehopt.o expr.o
flonum-copy.o flonum-konst.o flonum-mult.o frags.o hash.o input-file.o
input-scrub.o listing.o literal.o macro.o messages.o output-file.o read.o
remap.o sb.o stabs.o subsegs.o symbols.o write.o tc-i386.o obj-elf.o
atof-ieee.o  ../opcodes/.libs/libopcodes.a ../bfd/.libs/libbfd.a
-L/src/gcc/binutil-git/zlib -lz ../libiberty/libiberty.a -ldl
/home/git/binutils-gdb/bfd/compress.c: In function
'bfd_compress_section_contents':
/home/git/binutils-gdb/bfd/compress.c:161:4: error: 'zlib_size' may be used
uninitialized in this function [-Werror=maybe-uninitialized]
    memmove (buffer + compression_header_size,
    ^
/home/git/binutils-gdb/bfd/compress.c:88:7: note: 'zlib_size' was declared here
   int zlib_size;
       ^
lto1: all warnings being treated as errors
lto-wrapper: gcc returned 1 exit status
/usr/lib/gcc/x86_64-unknown-linux-gnu/4.9.2/../../../../x86_64-unknown-linux-gnu/bin/ld:
lto-wrapper failed
collect2: error: ld returned 1 exit status
Makefile:769: recipe for target 'as-new' failed
make[2]: *** [as-new] Error 1
make[2]: Leaving directory '/mnt/new/src/gcc/binutil-git/gas'


See also https://sourceware.org/bugzilla/show_bug.cgi?id=18313 .

[Bug lto/65991] maybe-unitialized - false positive

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65991

Markus Trippelsdorf <trippels at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |trippels at gcc dot gnu.org
         Resolution|---                         |INVALID

--- Comment #1 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
If you use custom CFLAGS when building binutils then configure with:
--disable-werror.

[Bug lto/65991] maybe-unitialized - false positive

[dilyan.palauzov at aegee dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65991

Дилян Палаузов <dilyan.palauzov at aegee dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|RESOLVED                    |UNCONFIRMED
         Resolution|INVALID                     |---

--- Comment #2 from Дилян Палаузов <dilyan.palauzov at aegee dot org> ---
Despite the custom CFLAGS used when building binutils, there is false positive
LTO warning.
>From gcc-bugs-return-485289-listarch-gcc-bugs=gcc.gnu.org@gcc.gnu.org Sun May 03 14:09:11 2015
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From: "trippels at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug lto/65991] maybe-unitialized - false positive
Date: Sun, 03 May 2015 14:09:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65991

Markus Trippelsdorf <trippels at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |WAITING
   Last reconfirmed|                            |2015-05-03
     Ever confirmed|0                           |1

--- Comment #3 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
(In reply to Дилян Палаузов from comment #2)
> Despite the custom CFLAGS used when building binutils, there is false
> positive LTO warning.

Well, first of all, please attach a small testcase as per
http://gcc.gnu.org/bugs.
And also note the word "maybe" in the warning. False positives are expected.

And finally this almost certainly a dup.
(Search existing bugs before opening new ones)
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From: "howarth.at.gcc at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/65931] [5/6 regression] dsymutil assertion failure building libgnat-5.dylib
Date: Sun, 03 May 2015 14:29:00 -0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?ide931

--- Comment #4 from Jack Howarth <howarth.at.gcc at gmail dot com> ---
(In reply to Dominique d'Humieres from comment #2)
> I have already filed Bug ID# 20510039 and I am using dsymutil from Xcode 6.2.

Did you also upload a standalone test case as a reproducer in that radar?

[Bug lto/65991] maybe-unitialized - false positive

[trippels at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65991

Markus Trippelsdorf <trippels at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|WAITING                     |RESOLVED
         Resolution|---                         |INVALID

--- Comment #4 from Markus Trippelsdorf <trippels at gcc dot gnu.org> ---
No feedback. Closing.

[Bug lto/65991] maybe-unitialized - false positive

[dilyan.palauzov at aegee dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65991

--- Comment #5 from Дилян Палаузов <dilyan.palauzov at aegee dot org> ---
The problem does not appear anymore, since I upgraded gcc 4.9.2 -> 4.9.3 .
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Subject: [Bug pch/14940] PCH largefile test fails on various platforms
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id\x14940

--- Comment #49 from Martin Richter <xricht17 at stud dot fit.vutbr.cz> ---
(In reply to Martin Richter from comment #47)

My apologies, that patch is incorrect - `VirtualAlloc` still uses
`pch_VA_max_size` instead of `size`.
Some discussion about this bug and the reasoning behind the patch can be found
here:
https://sourceforge.net/p/mingw-w64/bugs/382/


Now the correct patch:

diff --git a/gcc/config/i386/host-mingw32.c b/gcc/config/i386/host-mingw32.c
index aa17378..631d9c4 100644
--- a/gcc/config/i386/host-mingw32.c
+++ b/gcc/config/i386/host-mingw32.c
@@ -42,9 +42,6 @@ static size_t mingw32_gt_pch_alloc_granularity (void);

 static inline void w32_error(const char*, const char*, int, const char*);

-/* FIXME: Is this big enough?  */
-static const size_t pch_VA_max_size  = 128 * 1024 * 1024;
-
 /* Granularity for reserving address space.  */
 static size_t va_granularity = 0x10000;

@@ -86,9 +83,6 @@ static void *
 mingw32_gt_pch_get_address (size_t size, int)
 {
   void* res;
-  size = (size + va_granularity - 1) & ~(va_granularity - 1);
-  if (size > pch_VA_max_size)
-    return NULL;

   /* FIXME: We let system determine base by setting first arg to NULL.
      Allocating at top of available address space avoids unnecessary
@@ -98,7 +92,7 @@ mingw32_gt_pch_get_address (size_t size, int)
      If we allocate at bottom we need to reserve the address as early
      as possible and at the same point in each invocation. */

-  res = VirtualAlloc (NULL, pch_VA_max_size,
+  res = VirtualAlloc (NULL, size,
                      MEM_RESERVE | MEM_TOP_DOWN,
                      PAGE_NOACCESS);
   if (!res)
@@ -148,7 +142,7 @@ mingw32_gt_pch_use_address (void *addr, size_t size, int
fd,

   /* Offset must be also be a multiple of allocation granularity for
      this to work.  We can't change the offset. */
-  if ((offset & (va_granularity - 1)) != 0 || size > pch_VA_max_size)
+  if ((offset & (va_granularity - 1)) != 0)
     return -1;