forked from OSchip/llvm-project
a954bb18b1
Similar to D69607 but for archive member extraction unrelated to GC. This patch adds --why-extract=.
Prior art:
GNU ld -M prints
```
Archive member included to satisfy reference by file (symbol)
a.a(a.o) main.o (a)
b.a(b.o) (b())
```
-M is mainly for input section/symbol assignment <-> output section mapping
(often huge output) and the information may appear ad-hoc.
Apple ld64
```
__Z1bv forced load of b.a(b.o)
_a forced load of a.a(a.o)
```
It doesn't say the reference file.
Arm's proprietary linker
```
Selecting member vsnprintf.o(c_wfu.l) to define vsnprintf.
...
Loading member vsnprintf.o from c_wfu.l.
definition: vsnprintf
reference : _printf_a
```
---
--why-extract= gives the user the full data (which is much shorter than GNU ld
-Map). It is easy to track a chain of references to one archive member with a
one-liner, e.g.
```
% ld.lld main.o a_b.a b_c.a c.a -o /dev/null --why-extract=- | tee stdout
reference extracted symbol
main.o a_b.a(a_b.o) a
a_b.a(a_b.o) b_c.a(b_c.o) b()
b_c.a(b_c.o) c.a(c.o) c()
% ruby -ane 'BEGIN{p={}}; p[$F[1]]=[$F[0],$F[2]] if $.>1; END{x="c.a(c.o)"; while y=p[x]; puts "#{y[0]} extracts #{x} to resolve #{y[1]}"; x=y[0] end}' stdout
b_c.a(b_c.o) extracts c.a(c.o) to resolve c()
a_b.a(a_b.o) extracts b_c.a(b_c.o) to resolve b()
main.o extracts a_b.a(a_b.o) to resolve a
```
Archive member extraction happens before --gc-sections, so this may not be a live path
under --gc-sections, but I think it is a good approximation in practice.
* Specifying a file avoids output interleaving with --verbose.
* Required `=` prevents accidental overwrite of an input if the user forgets `=`. (Most of compiler drivers' long options accept `=` but not ` `)
Differential Revision: https://reviews.llvm.org/D109572
|
||
|---|---|---|
| .. | ||
| Arch | ||
| AArch64ErrataFix.cpp | ||
| AArch64ErrataFix.h | ||
| ARMErrataFix.cpp | ||
| ARMErrataFix.h | ||
| CMakeLists.txt | ||
| CallGraphSort.cpp | ||
| CallGraphSort.h | ||
| Config.h | ||
| DWARF.cpp | ||
| DWARF.h | ||
| Driver.cpp | ||
| Driver.h | ||
| DriverUtils.cpp | ||
| EhFrame.cpp | ||
| EhFrame.h | ||
| ICF.cpp | ||
| ICF.h | ||
| InputFiles.cpp | ||
| InputFiles.h | ||
| InputSection.cpp | ||
| InputSection.h | ||
| LTO.cpp | ||
| LTO.h | ||
| LinkerScript.cpp | ||
| LinkerScript.h | ||
| MapFile.cpp | ||
| MapFile.h | ||
| MarkLive.cpp | ||
| MarkLive.h | ||
| Options.td | ||
| OutputSections.cpp | ||
| OutputSections.h | ||
| README.md | ||
| Relocations.cpp | ||
| Relocations.h | ||
| ScriptLexer.cpp | ||
| ScriptLexer.h | ||
| ScriptParser.cpp | ||
| ScriptParser.h | ||
| SymbolTable.cpp | ||
| SymbolTable.h | ||
| Symbols.cpp | ||
| Symbols.h | ||
| SyntheticSections.cpp | ||
| SyntheticSections.h | ||
| Target.cpp | ||
| Target.h | ||
| Thunks.cpp | ||
| Thunks.h | ||
| Writer.cpp | ||
| Writer.h | ||
README.md
See docs/NewLLD.rst