[Bug lto/83967] New: LTO removes C functions declared as weak in assembler(depending on files order in linking)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83967 Bug ID: 83967 Summary: LTO removes C functions declared as weak in assembler(depending on files order in linking) Product: gcc Version: 7.2.1 Status: UNCONFIRMED Severity: normal Priority: P3 Component: lto Assignee: unassigned at gcc dot gnu.org Reporter: hurwic8 at gmail dot com CC: marxin at gcc dot gnu.org Target Milestone: --- I've observed strange behaviour of the link-time optimization on GCC 7.2.1, exact version: gcc version 7.2.1 20170904 (release) [ARM/embedded-7-branch revision 255204] (GNU Tools for Arm Embedded Processors 7-2017-q4-major) I have project that is compiled for the microcontroller. In startup file, that is written in assembler, there are weak definitions of the interrupt handlers. Some of those weak functions are defined in the project C files. Strange behaviour occurs when I set -flto flag on GCC 7.2.1: during optimization, the defined in C files interrupt functions are perceived as unused and removed(replaced by its weak definitions) - I've checked that in the .map file. This issue does not occur when startup file is first on the source files list, which is given as an argument to the linker. If I change order of source files, all interrupt handlers from C files, that are placed on the source files list before startup are removed and replaced by weak definitions from startup. For me it seems that linker is removing interrupt handler functions before noticing its usage in startup file. Or maybe weak function definitions from startup override definitions from C files. I've checked if this issue happens on the GCC 4.9.3 - it worked fine, so this is rather new behaviour. I've also confirmed this bug with other developer from Germany: https://www.mikrocontroller.net/topic/443262 Take a look at the latest posts, which are written in English. Is this a bug or should I place some extra pragmas/attributes to extort proper linker behaviour? Please let me know if you want me to prepare some basic examples of this issue.
[Bug lto/83967] LTO removes C functions declared as weak in assembler(depending on files order in linking)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83967 --- Comment #4 from Rafał Mszal --- Created attachment 43210 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43210&action=edit Basic example of main funtion with LTO failure. This is simple example of observed LTO issue. RTC1_IRQHandler is removed despite it is used to change volatile variable. RTC1_IRQHandler is defined weak in the assembler startup file.
[Bug lto/83967] LTO removes C functions declared as weak in assembler(depending on files order in linking)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83967 --- Comment #5 from Rafał Mszal --- Created attachment 43211 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43211&action=edit Makefile that causes failure.
[Bug lto/83967] LTO removes C functions declared as weak in assembler(depending on files order in linking)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83967 --- Comment #6 from Rafał Mszal --- Created attachment 43212 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43212&action=edit Startup file for the nRF52 microcontroller. This is typical startup for nRF5x microcontrollers. The main thing that is important is the interrupts vector table. All interrupts used in table are declared as weak at the end of file.
[Bug lto/83967] LTO removes C functions declared as weak in assembler(depending on files order in linking)
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83967 --- Comment #7 from Rafał Mszal --- Thanks for response. I've send some basic example of the failure. However, it needs some others file to compile and link, like linker, SystemInit function decalration and so on. I've just send you most important files, now I am working on removing sources that are not important, but this will take me a while, since i need to remove lot of dependencies between those files, makefile and linker. I've checked 'used' attribute, it doesn't solve the problem. Same with the suggested '-fuse-linker-plugin' flag.
