Re: linux-next failing build due to missing cubictcp_state symbol
From: Jiri Olsa <hidden>
Date: 2021-05-03 10:08:25
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On Mon, May 03, 2021 at 10:59:44AM +0200, Jiri Slaby wrote:
CCing pahole people. On 03. 05. 21, 9:59, Jiri Slaby wrote:quoted
On 03. 05. 21, 8:11, Jiri Slaby wrote:quoted
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looks like vfs_truncate did not get into BTF data, I'll try to reproduce_None_ of the functions are generated by pahole -J from debuginfo on ppc64. debuginfo appears to be correct. Neither pahole -J fs/open.o works correctly. collect_functions in dwarves seems to be defunct on ppc64... "functions" array is bogus (so find_function -- the bsearch -- fails).It's not that bogus. I forgot an asterisk:quoted
#0 find_function (btfe=0x100269f80, name=0x10024631c "stream_open") at /usr/src/debug/dwarves-1.21-1.1.ppc64/btf_encoder.c:350 (gdb) p (*functions)@84 $5 = {{name = 0x7ffff68e0922 ".__se_compat_sys_ftruncate", addr = 75232, size = 72, sh_addr = 65536, generated = false}, { name = 0x7ffff68e019e ".__se_compat_sys_open", addr = 80592, size = 216, sh_addr = 65536, generated = false}, { name = 0x7ffff68e0076 ".__se_compat_sys_openat", addr = 80816, size = 232, sh_addr = 65536, generated = false}, { name = 0x7ffff68e0908 ".__se_compat_sys_truncate", addr = 74304, size = 100, sh_addr = 65536, generated = false}, {...quoted
name = 0x7ffff68e0808 ".stream_open", addr = 65824, size = 72, sh_addr = 65536, generated = false}, {...quoted
name = 0x7ffff68e0751 ".vfs_truncate", addr = 73392, size = 544, sh_addr = 65536, generated = false}}The dot makes the difference, of course. The question is why is it there? I keep looking into it. Only if someone has an immediate idea...Well, .vfs_truncate is in .text (and contains an ._mcount call). And vfs_truncate is in .opd (w/o an ._mcount call). Since setup_functions excludes all functions without the ._mcount call, is_ftrace_func later returns false for such functions and they are filtered before the BTF processing. Technically, get_vmlinux_addrs looks at a list of functions between __start_mcount_loc and __stop_mcount_loc and considers only the listed. I don't know what the correct fix is (exclude .opd functions from the filter?). Neither why cross compiler doesn't fail, nor why ebi v2 avoids this too.Attaching a patch for pahole which fixes the issue, but I have no idea whether it is the right fix at all.
hi, we're considering to disable ftrace filter completely, I guess that would solve this issue for ppc as well https://lore.kernel.org/bpf/20210501001653.x3b4rk4vk4iqv3n7@kafai-mbp.dhcp.thefacebook.com/ (local) jirka
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regards,--js suse labs
quoted hunk ↗ jump to hunk
From: Jiri Slaby <redacted> Subject: ppc64: .opd section fix Patch-mainline: submitted 2021/05/03 Functions in the .opd section should be considered valid too. Otherwise, pahole cannot produce a .BTF section from vmlinux and kernel build fails on ppc64. --- btf_encoder.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-)--- a/btf_encoder.c +++ b/btf_encoder.c@@ -31,6 +31,8 @@ struct funcs_layout { unsigned long mcount_start; unsigned long mcount_stop; unsigned long mcount_sec_idx; + unsigned long opd_start; + unsigned long opd_stop; }; struct elf_function {@@ -271,11 +273,24 @@ static int is_ftrace_func(struct elf_fun return start <= addrs[r] && addrs[r] < end; } +static int is_opd_func(struct elf_function *func, struct funcs_layout *fl) +{ + return fl->opd_start <= func->addr && func->addr < fl->opd_stop; +} + static int setup_functions(struct btf_elf *btfe, struct funcs_layout *fl) { __u64 *addrs, count, i; int functions_valid = 0; bool kmod = false; + GElf_Shdr shdr; + Elf_Scn *sec; + + sec = elf_section_by_name(btfe->elf, &btfe->ehdr, &shdr, ".opd", NULL); + if (sec) { + fl->opd_start = shdr.sh_addr; + fl->opd_stop = shdr.sh_addr + shdr.sh_size; + } /* * Check if we are processing vmlinux image and@@ -322,7 +337,8 @@ static int setup_functions(struct btf_el func->addr += func->sh_addr; /* Make sure function is within ftrace addresses. */ - if (is_ftrace_func(func, addrs, count)) { + if (is_opd_func(func, fl) || + is_ftrace_func(func, addrs, count)) { /* * We iterate over sorted array, so we can easily skip * not valid item and move following valid field into