Changes/MingwMiniDebugInfo

MinGW MiniDebugInfo

Summary

Analogously to the MiniDebugInfo change for native packages, install minimal debuginfos by default also for MinGW packages.

Owner

• Name: Sandro Mani
• Email: <manisandro@gmail.com>
• Release notes owner:

Current status

• Targeted release: Fedora 28
• Last updated: 2017-08-30
• Tracker bug: <will be assigned by the Wrangler>

Detailed Description

Currently the debuginfo data of MinGW binaries is completely stripped from the binary and placed in the respective .debuginfo file. This change proposes keeping the PE symbols in the binary, similarly to what was done for native binaries.

The change basically involves changing mingw-find-debuginfo.sh as follows:

diff --git a/mingw-filesystem/mingw-find-debuginfo.sh b/mingw-filesystem/mingw-find-debuginfo.sh
index de6dee1..261385f 100755
--- a/mingw-filesystem/mingw-find-debuginfo.sh
+++ b/mingw-filesystem/mingw-find-debuginfo.sh
@@ -25,7 +25,10 @@ do
        echo extracting debug info from $f
        mingw-objcopy --only-keep-debug $f $f.debug || :
        pushd `dirname $f`
-       mingw-objcopy --add-gnu-debuglink=`basename $f.debug` --strip-unneeded `basename $f` || :
+       keep_symbols=`mktemp`
+  mingw-nm $f.debug --format=sysv --defined-only | awk -F \| '{ if ($4 ~ "Function") print $1 }' | sort > "$keep_symbols"
+       mingw-objcopy --add-gnu-debuglink=`basename $f.debug` --strip-unneeded `basename $f` --keep-symbols="$keep_symbols" || :
+       rm -f "$keep_symbols"
        popd
 done

A test with some packages in this COPR repo shows that the price is a size increase of in average 17%:

Binary	Stripped size	Size with symbols	Relative size change
libgio-2.0-0.dll	1412	1656	117.28%
libglib-2.0-0.dll	1092	1184	108.42%
libgmodule-2.0-0.dll	28	32	114.29%
libgobject-2.0-0.dll	312	352	112.82%
libgiomm-2.4-1.dll	1284	1732	134.89%
libglibmm-2.4-1.dll	432	588	136.11%
Qt5Concurrent.dll	36	44	122.22%
Qt5Core.dll	4884	5508	112.78%
Qt5DBus.dll	548	652	118.99%
Qt5Gui.dll	4408	5208	118.15%
Qt5Network.dll	1568	1892	120.66%
Qt5OpenGL.dll	328	404	123.17%
Qt5PrintSupport.dll	376	448	119.15%
Qt5Sql.dll	268	312	116.42%
Qt5Test.dll	252	284	112.70%
Qt5Widgets.dll	5716	6768	118.40%
Qt5Xml.dll	216	268	124.07%

Benefit to Fedora

Make it easier to debug Windows applications cross-compiled from Fedora, in particular:

• A convenient way to manage crash reporting is to ship gdb with the application, and in case of a crash, attach it to the dying process, collect a stacktrace, and ask the user to send it to the developer. For the developer it helps plenty if the stacktrace already contained symbol names, instead of being number-only.
• If you need to live-debug a deployed system, it is not always easy to obtain the correct debuginfo packages and install them along the binaries.

Scope

• Proposal owners:
  • Change mingw-binutils toalso install a generic mingw-nm, which will be used by mingw-find-debuginfo.sh
  • Change mingw-find-debuginfo.sh as outlined above
  • Rebuild all mingw packages

• Other developers: N/A (not a System Wide Change)

• Release engineering: #7005 (a check of an impact with Release Engineering is needed)
  • List of deliverables: N/A (not a System Wide Change)

• Policies and guidelines: N/A (not a System Wide Change)

• Trademark approval: N/A (not needed for this Change)

Upgrade/compatibility impact

N/A (not a System Wide Change)

How To Test

• Wait for the packages rebuilt with the new mingw-find-debuginfo.sh to land, or use the test packages in this COPR repo.
• Make a Windows application using the binaries with minidebug infos crash
• The stacktrace should contain function names, i.e.

#0  0x000000000040157d in foo() ()
#1  0x00000000004015b5 in main () 

as opposed to being number only:

#0  0x000000000040157d in ?? ()
#1  0x00000000004015b5 in ?? ()
#2  0x00000000004013f7 in ?? ()
#3  0x000000000040152b in ?? ()
#4  0x0000000076af652d in KERNEL32!BaseThreadInitThunk ()
   from C:\Windows\system32\kernel32.dll
#5  0x0000000076d2c521 in ntdll!RtlUserThreadStart ()
   from C:\Windows\SYSTEM32\ntdll.dll
#6  0x0000000000000000 in ?? ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)

User Experience

N/A (not a System Wide Change)

Dependencies

N/A (not a System Wide Change)

Contingency Plan

• Contingency mechanism: N/A (not a System Wide Change)
• Contingency deadline: N/A (not a System Wide Change)
• Blocks release? N/A (not a System Wide Change), Yes/No
• Blocks product? none

Documentation

N/A (not a System Wide Change)

Release Notes

MinGW binaries contain symbol names by default for easier debugging.