Hi,
Here is a proposal to update LTO plugin interface. Any comments?
Thanks.
--
H.J.
---
Goal: We should preserve the same linker command line order as if
there are no IR.
Problem:
a. LTO may generate extra symbol references which aren't in IR.
b. It was worked around with -pass-through hack. But it doesn't
preserve the link command line order.
Proposal:
a. Remove -pass-through hack in GCC.
b. Compiler plugin controls what linker uses to generate the final
executable:
i. The linker command line order should be the same, with or
without LTO.
c. Add a cmdline bit field to
struct ld_plugin_input_file
{
const char *name;
int fd;
off_t offset;
off_t filesize;
void *handle;
unsigned int cmdline : 1;
};
It is used by linker to tell plugin that the input file comes from
linker command line.
d. 2 stage linker:
i. Stage 1: Normal symbol resolution with plugin.
ii. Stage 2:
1) Call the "all symbols read" handler to get the final
linker inputs.
2) Discard all previous inputs.
3) Generate the final executable with inputs from
plugin.
e. Compiler plugin:
i. For a file, which comes from the linker command line and
isn't
claimed by plugin, save it in the linker pass-through list in the same
order as it comes in.
ii. For the first file claimed by plugin, remember the last
pass-through linker input.
iii. The "all symbols read" handler adds input files to the
linker
in the order:
1) All linker input files on the linker pass-through
list up to the
first file claimed by plugin.
2) All linker input files generated by plugin.
3) The rest of linker input files on the linker
pass-through list.
f. Limitation:
i. All files claimed by plugin are grouped together. Any
archives
between files claimed by plugin are placed after all linker input
files generated by plugin when passed to linker.
