2009/3/15 Wolfgang Glas <wolfgang.g...@ev-i.at>:
> Hi all,
>
> I've been trying very hard to reduce my alloca() problems and at got stuck
> with every attempt to isolate the problem.
>
> Finally I linked a mildly complex C-program, which crashed before using a
> handcrafted Makefile and luckily I found out, that the program crashes, when I
> add a bunch Window's system libraries to the linker command line. (A practice
> I
> cowardly copied from another project years ago...)
>
> I've uploaded a self-contained (but not small) testcase to our weebserver
> under
>
> http://www.ev-i.at/tmp/mingw_hpgspdf_test.tar.gz
>
> The makefile generates two executables: One linked just with the
> self-generated
> DLLs and one linked with a long list of windows system libraries. The
> executable
> linked with the windows libraries is called hpgspdffile-read-fail.exe and has
> a
> different size than the executable hpgspdffile-read.exe linked with just the
> self-generated libraries. Besides, it has the same runtime dependencies and
> however it *does* crash right after alloca(), while the other one survives
> flawlessly.
>
> The program reads a PDF-file, interprets it's internal structure and
> re-serializes the file afterwards. (Should work with any normal PDF-file).
>
> This is my debug-session:
>
> **************************************
> H:\wglas\CC\mingw_hpgspdf_test\bin64>gdb-w64 .\hpgspdffile-read-fail.exe
> GNU gdb 6.7.50.20080109-cvs
> Copyright (C) 2008 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
> This is free software: you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law. Type "show copying"
> and "show warranty" for details.
> This GDB was configured as "x86_64-pc-mingw32"...
>
> warning: A handler for the OS ABI "Cygwin" is not built into this
> configuration
> of GDB. Attempting to continue with the default i386:x86-64 settings.
>
> (gdb) break hpgspdffile.c:1230
> Breakpoint 1 at 0x40eead: file hpgspdffile.c, line 1230.
> (gdb) r H:\wglas\doc\hp\bpl13205.pdf x.pdf
> Starting program:
> H:\wglas\CC\mingw_hpgspdf_test\bin64/.\hpgspdffile-read-fail.e
> xe H:\wglas\doc\hp\bpl13205.pdf x.pdf
> len=28.
> value=C:\Program Files (x86)\cdes.
> prefix=C:\Program Files (x86)\cdes.
> Opening file H:\wglas\doc\hp\bpl13205.pdf.
> Reading file H:\wglas\doc\hp\bpl13205.pdf.
>
> Breakpoint 1, hpgs_pdf_file_read_xref (pdf=0x3f7720) at hpgspdffile.c:1230
> 1230 hpgspdffile.c: No such file or directory.
> in hpgspdffile.c
> (gdb) print tail_data
> $1 = 0x22fda0 ""
> (gdb) print &len
> $2 = (size_t *) 0x22fdb0
> (gdb) n
>
> Program received signal SIGSEGV, Segmentation fault.
> 0x000007ff7fc52806 in ?? ()
> (gdb) bt
> #0 0x000007ff7fc52806 in ?? ()
> #1 0x000007ff7fc4a949 in ?? ()
> #2 0x0000000000000003 in ?? ()
> #3 0x0000000000000003 in ?? ()
> #4 0x0000000000000003 in ?? ()
> #5 0x000000000033d627 in ?? ()
> #6 0x0000000000000000 in ?? ()
> (gdb) q
> The program is running. Exit anyway? (y or n) y
>
> H:\wglas\CC\mingw_hpgspdf_test\bin64>
> **************************************
>
> Explanation:
>
> tail_data is a char-array of size 2048, which has been allocated through
> alloca(), 'len' is a local variable. The problem her is, that alloca() places
> tail_data 16 bytes before len, which is far less than the required 2048
> bytes...
>
> Hopefully, this will bring us one step further in resolving this curious
> problem.
>
> Regards,
>
> Wolfgang
>
>
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By trying to reduce this test case I stumble over the assembly produced
leaq 30(%rbx), %rax
andq $-16, %rax
call ___chkstk
so, if %rbx is zero (len == 0) this happens what you are describing.
that tail_data is just 16 bytes away from file_len. So possibly you
should check the result of hpgs_istream_tell(pdf->is,&file_len), if
file_len is not equal to zero. If it is, all points to an alias issue.
Cheers,
Kai
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Apps built with the Adobe(R) Flex(R) framework and Flex Builder(TM) are
powering Web 2.0 with engaging, cross-platform capabilities. Quickly and
easily build your RIAs with Flex Builder, the Eclipse(TM)based development
software that enables intelligent coding and step-through debugging.
Download the free 60 day trial. http://p.sf.net/sfu/www-adobe-com
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