| Summary: | usage tracking by --gc-sections ignores a --defsym mapping | ||
|---|---|---|---|
| Product: | binutils | Reporter: | Don Kinzer <dkinzer> |
| Component: | ld | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED FIXED | ||
| Severity: | normal | CC: | amodra, nickc |
| Priority: | P2 | ||
| Version: | 2.19 | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Last reconfirmed: | ||
| Attachments: |
test case makefile and C source
test case makefile test case C source Re-evaluate --defsym options early lang_do_assignments |
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Created attachment 6209 [details]
test case makefile
Created attachment 6210 [details]
test case C source
Created attachment 6212 [details]
Re-evaluate --defsym options
Hi Don, Please could you try out the uploaded patch and let me know if it works for you. Cheers Nick Thanks for the quick response on this. The version of avr-ld that I am using is part of the WinAVR_20100110 release but I'll see if I can build the equivalent avr-ld from sources+patches and then add your patch. Regards, Don Kinzer Nick, can you just run lang_do_assignments before lang_gc_sections instead? Hi Alan,
> can you just run lang_do_assignments before lang_gc_sections instead?
I tried that, but could not find a way to make it work. If you run it with lang_first_phase_enum it does not recompute the defsym assignments. If you run it with any other enum it fails the "output section size must be non-zero" assertion in lamg_size_sections_1.
I agree however that re-invoking lang_do_assignments would be a better way to fix the problem. I will investigate some more and see if I can persuade it to work.
Cheers
Nick
I back-ported the patch to ld 2.19.1. In doing so, I had to modify the patch slightly because that version of the source doesn't have the function exp_defsym(). I created a similar function and changed the yacc grammar action to invoke it when the --defsym option is seen. In testing, I can see that a defsym_node structure is created and put on the defsym_list list. Further, that single node is processed when ldexp_rerun_defsyms() is called and the two conditions therein are true allowing exp_fold_tree() to be called. This all suggests that I've patched my version correctly but the resulting executable image is the same as before: 000000c8 <main>: c8: 9b df rcall .-202 ; 0x0 <__vectors> ca: ff cf rjmp .-2 ; 0xca <main+0x2> If it works on your version of ld then it appears that there may be other changes required for v2.19.1. Regards, Don Kinzer Created attachment 6215 [details]
early lang_do_assignments
This also seems to work.
Hmm, running lang_do_assignments before lang_gc_sections does change a few things in the symbol table, leading to some cris-elf testsuite failures. What's happening is that elf_gc_sweep now sees all the link script defined symbols, so they become subject to garbage collecting (well, forcing local). For the first test that fails, the expected symbol table is SYMBOL TABLE: 00080074 l d .text 00000000 .text 00082078 l d .got 00000000 .got 00082078 l O .got 00000000 _GLOBAL_OFFSET_TABLE_ 00080074 g .text 00000000 _start 00082084 g *ABS* 00000000 __bss_start 00082084 g *ABS* 00000000 _edata 000820a0 g *ABS* 00000000 _end but we now get SYMBOL TABLE: 00080074 l d .text 00000000 .text 00082078 l d .got 00000000 .got 00082084 l *ABS* 00000000 __bss_start 00082084 l *ABS* 00000000 _edata 00082078 l O .got 00000000 _GLOBAL_OFFSET_TABLE_ 000820a0 l *ABS* 00000000 _end 00080074 g .text 00000000 _start Note how __bss_start, _edata, _end are now local since no dynamic objects referred to them. I don't think that is a great concern, but of course means tweaking the cris testsuite when/if this patch goes in. CVSROOT: /cvs/src Module name: src Changes by: nickc@sourceware.org 2012-02-22 16:27:35 Modified files: ld : ChangeLog ldexp.c ldexp.h ldlang.c ld/testsuite : ChangeLog ld/testsuite/ld-cris: tls-gc-68.d tls-gc-69.d tls-gc-70.d tls-gc-71.d tls-gc-75.d tls-gc-76.d tls-gc-79.d ld/testsuite/ld-gc: gc.exp Added files: ld/testsuite/ld-gc: pr13683.c pr13683.d Log message: PR ld/13683 * ldlang.c (lang_process): Rerun lang_do_assignments before starting garbage collection. * ldexp.c (fold_name): Generate a reloc for defined symbols found without an associated output section during the mark phase. (exp_fold_tree_1): Continue processing an expression, even if we are unable to fold it, if we are in the first two evaluation phases. * ldexp.h (enum lang_phase_type): Add descriptions of the phases. * ld-gc/pr13683.c: New test source file. * ld-gc/pr13683.d: New test control and output file. * ld-gc/gc.exp: Run the pr13683 test. * ld-cris/tls-gc-68: Update expected symbol table dump. * ld-cris/tls-gc-69: Likewise. * ld-cris/tls-gc-70: Likewise. * ld-cris/tls-gc-71: Likewise. * ld-cris/tls-gc-75: Likewise. * ld-cris/tls-gc-76.d: Likewise. * ld-cris/tls-gc-79.d: Likewise. Patches: http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/ChangeLog.diff?cvsroot=src&r1=1.2410&r2=1.2411 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/ldexp.c.diff?cvsroot=src&r1=1.96&r2=1.97 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/ldexp.h.diff?cvsroot=src&r1=1.30&r2=1.31 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/ldlang.c.diff?cvsroot=src&r1=1.383&r2=1.384 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/testsuite/ChangeLog.diff?cvsroot=src&r1=1.1494&r2=1.1495 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/testsuite/ld-cris/tls-gc-68.d.diff?cvsroot=src&r1=1.2&r2=1.3 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/testsuite/ld-cris/tls-gc-69.d.diff?cvsroot=src&r1=1.2&r2=1.3 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/testsuite/ld-cris/tls-gc-70.d.diff?cvsroot=src&r1=1.2&r2=1.3 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/testsuite/ld-cris/tls-gc-71.d.diff?cvsroot=src&r1=1.1&r2=1.2 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/testsuite/ld-cris/tls-gc-75.d.diff?cvsroot=src&r1=1.2&r2=1.3 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/testsuite/ld-cris/tls-gc-76.d.diff?cvsroot=src&r1=1.2&r2=1.3 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/testsuite/ld-cris/tls-gc-79.d.diff?cvsroot=src&r1=1.2&r2=1.3 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/testsuite/ld-gc/pr13683.c.diff?cvsroot=src&r1=NONE&r2=1.1 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/testsuite/ld-gc/pr13683.d.diff?cvsroot=src&r1=NONE&r2=1.1 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/testsuite/ld-gc/gc.exp.diff?cvsroot=src&r1=1.12&r2=1.13 Hi Guys, Alan's patch is better than mine, so I have checked it in, along with a new linker testcase and some tweaks to the cris linker tests that were affected. (No other target showed regressions because of this patch). Cheers Nick CVSROOT: /cvs/src Module name: src Changes by: amodra@sourceware.org 2012-03-05 23:09:11 Modified files: ld/testsuite : ChangeLog ld/testsuite/ld-gc: pr13683.d Log message: PR ld/13683 * ld-gc/pr13683.d: Allow non-zero top address digit. Patches: http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/testsuite/ChangeLog.diff?cvsroot=src&r1=1.1498&r2=1.1499 http://sourceware.org/cgi-bin/cvsweb.cgi/src/ld/testsuite/ld-gc/pr13683.d.diff?cvsroot=src&r1=1.1&r2=1.2 |
Created attachment 6208 [details] test case makefile and C source I have a use case where I need to perform link-time mapping of a function call to one of several differently named candidates having the same parameter lists and return type. In the actual use case all of the candidate functions are in a library but that fact is not relevant to the problem that arises. The attached .c and makefile can be used to observe the problem when compiled for an AVR target. In this simple test case, main calls a non-existent function "foo" and the linker option --defsym,foo=foo2 is used to map the call to the desired function. If the link step is performed without the --gc-sections option, the resulting executable is correct as shown in this .lss excerpt: 000000e0 <main>: e0: f7 df rcall .-18 ; 0xd0 <foo2> e2: ff cf rjmp .-2 ; 0xe2 <main+0x2> However, adding --gc-sections to the link options produces this incorrect code with no warning or error messages: 000000c8 <main>: c8: 9b df rcall .-202 ; 0x0 <__vectors> ca: ff cf rjmp .-2 ; 0xca <main+0x2> The resulting load image contains none of the three candidate functions indicating the the linker code that eliminates unused functions determined that they were all unused even though "foo2" should have been marked as used. I attempted to confirm this issue for an x86 target (ld v2.21.1) but it appeared that --gc-sections didn't remove any unused functions.