apache
issue with c++ exceptions support + elf loading
When we are trying to build elf along with exceptions (stm32f4discovery elf config with uClib++ and exceptions enabled), some extra sections are getting created (without following the linker script).
abhishek@Linux:~/Work/public/nuttx_build/apps$ readelf -S --wide libapps.a
.
.
.
File: libapps.a(helloxx_main.cxx.home.abhishek.Work.public.nuttx_build.apps.examples.helloxx_1.o)
There are 34 section headers, starting at offset 0xa00:
Section Headers:
[Nr] Name Type Addr Off Size ES Flg Lk Inf Al
[ 0] NULL 00000000 000000 000000 00 0 0 0
[ 1] .group GROUP 00000000 000034 000014 04 31 37 4
[ 2] .text PROGBITS 00000000 000048 000000 00 AX 0 0 1
[ 3] .data PROGBITS 00000000 000048 000000 00 WA 0 0 1
[ 4] .bss NOBITS 00000000 000048 000000 00 WA 0 0 1
[ 5] .text._ZN11CHelloWorldD2Ev PROGBITS 00000000 000048 000002 00 AXG 0 0 2
[ 6] .ARM.extab.text._ZN11CHelloWorldD2Ev PROGBITS 00000000 00004a 000000 00 AG 0 0 1
[ 7] .ARM.exidx.text._ZN11CHelloWorldD2Ev ARM_EXIDX 00000000 00004c 000008 00 ALG 5 0 4
[ 8] .rel.ARM.exidx.text._ZN11CHelloWorldD2Ev REL 00000000 0006b4 000008 08 IG 31 7 4
[ 9] .rodata._ZN11CHelloWorld10HelloWorldEv.isra.0.str1.1 PROGBITS 00000000 000054 000056 01 AMS 0 0 1
[10] .text._ZN11CHelloWorld10HelloWorldEv.isra.0 PROGBITS 00000000 0000ac 000018 00 AX 0 0 4
[11] .rel.text._ZN11CHelloWorld10HelloWorldEv.isra.0 REL 00000000 0006bc 000018 08 I 31 10 4
[12] .ARM.extab.text._ZN11CHelloWorld10HelloWorldEv.isra.0 PROGBITS 00000000 0000c4 000000 00 A 0 0 1
[13] .ARM.exidx.text._ZN11CHelloWorld10HelloWorldEv.isra.0 ARM_EXIDX 00000000 0000c4 000008 00 AL 10 0 4
[14] .rel.ARM.exidx.text._ZN11CHelloWorld10HelloWorldEv.isra.0 REL 00000000 0006d4 000008 08 I 31 13 4
[15] .rodata.helloxx_main.str1.1 PROGBITS 00000000 0000cc 0000cf 01 AMS 0 0 1
[16] .text.helloxx_main PROGBITS 00000000 00019c 000058 00 AX 0 0 4
[17] .rel.text.helloxx_main REL 00000000 0006dc 000040 08 I 31 16 4
[18] .ARM.extab.text.helloxx_main PROGBITS 00000000 0001f4 000000 00 A 0 0 1
[19] .ARM.exidx.text.helloxx_main ARM_EXIDX 00000000 0001f4 000008 00 AL 16 0 4
[20] .rel.ARM.exidx.text.helloxx_main REL 00000000 00071c 000010 08 I 31 19 4
[21] .text.startup._GLOBAL__sub_I_helloxx_main PROGBITS 00000000 0001fc 000020 00 AX 0 0 4
[22] .rel.text.startup._GLOBAL__sub_I_helloxx_main REL 00000000 00072c 000020 08 I 31 21 4
[23] .ARM.extab.text.startup._GLOBAL__sub_I_helloxx_main PROGBITS 00000000 00021c 000000 00 A 0 0 1
[24] .ARM.exidx.text.startup._GLOBAL__sub_I_helloxx_main ARM_EXIDX 00000000 00021c 000008 00 AL 21 0 4
[25] .rel.ARM.exidx.text.startup._GLOBAL__sub_I_helloxx_main REL 00000000 00074c 000008 08 I 31 24 4
[26] .init_array INIT_ARRAY 00000000 000224 000004 04 WA 0 0 4
[27] .rel.init_array REL 00000000 000754 000008 08 I 31 26 4
[28] .bss._ZL12g_HelloWorld NOBITS 00000000 000228 000004 00 WA 0 0 4
[29] .comment PROGBITS 00000000 000228 00004a 01 MS 0 0 1
[30] .ARM.attributes ARM_ATTRIBUTES 00000000 000272 00002e 00 0 0 1
[31] .symtab SYMTAB 00000000 0002a0 000320 10 32 41 4
[32] .strtab STRTAB 00000000 0005c0 0000f1 00 0 0 1
[33] .shstrtab STRTAB 00000000 00075c 0002a1 00 0 0 1
Key to Flags:
W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
L (link order), O (extra OS processing required), G (group), T (TLS),
C (compressed), x (unknown), o (OS specific), E (exclude),
y (purecode), p (processor specific)
File: libapps.a(dummy.c.home.abhishek.Work.public.nuttx_build.apps.platform_1.o)
There are 9 section headers, starting at offset 0x16c:
.
.
But, as per the elf loader code, we are only considering one ARM.exidx section in up_init_exidx,
https://github.com/apache/nuttx/blob/72f9bd142f2f50bbd68548700c30be3b161462ff/binfmt/libelf/libelf_load.c#L408-L420
Why are the other sections not considered? Also, why is the out file not following the linker script, why are new sections created?
I have integrated the elf loading (binfmt/libelf) in my project and I am trying to enabled cpp exceptions. I am stuck with the issue I have mentioned above. I couldn't check if the config works fine as I don't have stm32f4discovery board but I am able to verify that the same sections are getting created in nuttx too. Is this expected behavior? Is there a way to avoid these additional sections?
I have fixed some build issues when building the above config in the below PRs.
https://github.com/apache/nuttx/pull/11688 https://github.com/apache/nuttx-apps/pull/2286
Also, to add, as I understand each text section has corresponding exidx and extab sections. Hence, wondering
- how and why the new extra text sections are created without following the linker script
- why are the additional exidx sections not taken care of during elf loading.
Thank you @abhishek-samsung ! I approved the first commit, but the second one seems incorrect
Hello @acassis , could you please help me with this issue? Are exceptions with elf loading working on any other ARM cortex M boards?
Also, I found that all the newly created sections have the SHF_GROUP flag. And its not handled in elf loading. Any guidance or reference on this would be very helpful.
Hi @abhishek-samsung I did a suggestion in your PR, maybe we could create a generic section that could be defined in the board linker script and that section will be just like an alias to the ARM section. I think this way we avoid polluting the generic linker script with arch specific sections. @xiaoxiang781216 @patacongo what do you think?
Since it's a common issue for all arm32 soc/chip, I would suggest that we should find a solution fix this problem for all board.
