Hello toolchain gurus, In the course of Linaro's kernel tinification project, the ability to compile the Linux kernel using LTO is a frequent requirement. However the kernel makes heavy usage of 'ld -r' with .o files resulting from LTO build of .c files as well as .o files resulting from pure assembly code.
This mix of LTO and non-LTO object files is not supported by upstream binutils unless a patch from H.J. Lu is applied. That patch has been available since 2013 and was last refreshed in his 2.25.51.0.4 branch last September. It is accessible here: https://git.linaro.org/toolchain/binutils-gdb.git/commit/6da5456971 I've attached a very simple test case demonstrating the problem. With the binutils-lto-mixed.patch applied, this test case compiles to a working executable. Otherwise compilation fails at the 'ld -r' step. One question and one request: - What, if anything, has prevented this patch from being merged in the master branch upstream? - In the mean time, could we include this patch in the Linaro binutils package and releases? Having this available in our toolchain releases would greatly simplify the LTO related work on the kernel. It was included in all binutils releases from H.J. Lu since 2013 and therefore has obtained significant exposure already. Thanks. Nicolas
lto-mixed-test.tgz
Description: application/gzip
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