• d-bugmail puremagic.com Jan 23 2007
• d-bugmail puremagic.com Mar 31 2007
• d-bugmail puremagic.com Apr 04 2007
• Frits van Bommel <fvbommel REMwOVExCAPSs.nl> Apr 04 2007
• d-bugmail puremagic.com Apr 25 2007
• d-bugmail puremagic.com Aug 29 2010

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=879

           Summary: support for --gc-sections
           Product: D
           Version: 1.00
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P3
         Component: DMD
        AssignedTo: bugzilla digitalmars.com
        ReportedBy: thomas-dloop kuehne.cn


--gc-sections is ld's flag to "Enable garbage collection of unused input 
sections."

As known(#100 and #101) it currently breaks DMD's exception handling on Linux. 
I think I've found the cause and know a simple fix.

#
# void main(){
#    throw new Exception("message");
# }
#

dmd a.d -ofa; nm --numeric-sort a
[...]
 000000000805c4b0 R _D3std6thread6Thread6__vtblZ
 000000000805c508 R _deh_beg
 000000000805c508 r _TMP3
 000000000805c514 r _TMP1


 000000000805c604 r _TMP14
 000000000805c610 r _TMP27
 000000000805c61c R _deh_end
 000000000805c61c r __FRAME_END__



dmd a.d -ofa -L--gc-sections; nm --numeric-sort a
 [...]
 0000000008053270 R _D3std6thread6Thread6__vtblZ
 00000000080532c8 R _deh_beg
 00000000080532c8 R _deh_end
 00000000080532c8 r __FRAME_END__
 [...]


The missing _TMP... symbols are of type internal.deh2.FuncTable and describe 
where to find the exception handlers of a given function.

BUG 1:
ld rightfully removed those as they are never directly referenced. However they 
are accessed indirectly via _deh_beg and _deh_end (-> internal/deh2.d:98-100).

FIX 1:
Define an elf symbol with the following characteristics:
address:  _deh_beg
size: _deh_end - _deh_beg + sizeof(_deh_end)
and ensure that this symbol is guaranteed to be referenced somewhere regardless 
of compiler flags like -O, -release and -inline.

BUG 2:
from above:
 00000000080532c8 R _deh_beg
 00000000080532c8 R _deh_end
 00000000080532c8 r __FRAME_END__


and _deh_end claim to be of size zero.

FIX 2:
The same as #472, please emit correct size information for all elf symbols.


-- 

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=879





------- Comment #1 from thomas-dloop kuehne.cn  2007-03-31 15:08 -------
Created an attachment (id=106)
 --> (http://d.puremagic.com/issues/attachment.cgi?id=106&action=view)
Binutils workaround


-- 

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=879





------- Comment #2 from thomas-dloop kuehne.cn  2007-04-04 15:39 -------
Daniel Jacobowitz suggested a much more straight forward solution on the 
binutils mailing list(http://sourceware.org/ml/binutils/):

 Another way to fix this would be to emit R_arch_NONE relocations from
 the code sections to the EH tables they require.



-- 

Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:

d-bugmail puremagic.com wrote:
 ------- Comment #2 from thomas-dloop kuehne.cn  2007-04-04 15:39 -------
 Daniel Jacobowitz suggested a much more straight forward solution on the 
 binutils mailing list(http://sourceware.org/ml/binutils/):
 
 Another way to fix this would be to emit R_arch_NONE relocations from
 the code sections to the EH tables they require.




Interesting. And should be easy enough to implement.
An added advantage to this approach would be that no relatively new 
version of binutils will be required to use --gc-sections[1], which 
might require working around (Linux) package managers.
It'd just a recent version of DMD (after this is implemented) which is 
more likely to be manually installed (and frequently updated) anyway.


[1]: (Assuming R_arch_NONE isn't a recent feature)

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=879





------- Comment #4 from thomas-dloop kuehne.cn  2007-04-25 12:56 -------
Walter, are you going to implement the R_arch_NONE solution or should we patch 
binutils?


-- 

d-bugmail puremagic.com writes:

http://d.puremagic.com/issues/show_bug.cgi?id=879


Brad Roberts <braddr puremagic.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |nfxjfg gmail.com


--- Comment #5 from Brad Roberts <braddr puremagic.com> 2010-08-29 12:35:37 PDT
---
*** Issue 4758 has been marked as a duplicate of this issue. ***

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