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2008-10-14ftrace: remove warning of old objcopy and local functionsSteven Rostedt
The warning messages about old objcopy and local functions spam the user quite drastically. Remove the warning until we can find a nicer way of tell the user to upgrade their objcopy. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-10-14ftrace: objcopy version test for local symbolsSteven Rostedt
The --globalize-symbols option came out in objcopy version 2.17. If the kernel is being compiled on a system with a lower version of objcopy, then we can not use the globalize / localize trick to link to symbols pointing to local functions. This patch tests the version of objcopy and will only use the trick if the version is greater than or equal to 2.17. Otherwise, if an object has only local functions within a section, it will give a nice warning and recommend the user to upgrade their objcopy. Leaving the symbols unrecorded is not that big of a deal, since the mcount record method changes the actual mcount code to be a simple "ret" without recording registers or anything. Reported-by: Stephen Rothwell <sfr@canb.auug.org.au> Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-10-14ftrace: handle weak symbol functionsSteven Rostedt
During tests and checks, I've discovered that there were failures to convert mcount callers into nops. Looking deeper into these failures, code that was attempted to be changed was not an mcount caller. The current code only updates if the code being changed is what it expects, but I still investigate any time there is a failure. What was happening is that a weak symbol was being used as a reference for other mcount callers. That weak symbol was also referenced elsewhere so the offsets were using the strong symbol and not the function symbol that it was referenced from. This patch changes the setting up of the mcount_loc section to search for a global function that is not weak. It will pick a local over a weak but if only a weak is found in a section, a warning is printed and the mcount location is not recorded (just to be safe). Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-10-14ftrace: update recordmount.pl arch changesSteven Rostedt
I'm trying to keep all the arch changes in recordmcount.pl in one place. I moved your code into that area, by adding the flags to the commands that were passed in. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-10-14ftrace: scripts/recordmcount.pl cross-build hackIngo Molnar
hack around: ld: Relocatable linking with relocations from format elf32-i386 (init/.tmp_gl_calibrate.o) to format elf64-x86-64 (init/.tmp_mx_calibrate.o) i CC arch/x86/mm/extable.o objcopy: 'init/.tmp_mx_calibrate.o': No such file rm: cannot remove `init/.tmp_mx_calibrate.o': No such file or directory ld: Relocatable linking with relocations from format elf32-i386 (arch/x86/mm/extable.o) to format elf64-x86-64 (arch/x86/mm/.tmp_mx_extable.o) is not supported mv: cannot stat `arch/x86/mm/.tmp_mx_extable.o': No such file or directory ld: Relocatable linking with relocations from format elf32-i386 (arch/x86/mm/fault.o) to format elf64-x86-64 (arch/x86/mm/.tmp_mx_fault.o) is not supported Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-10-14ftrace: create __mcount_loc sectionSteven Rostedt
This patch creates a section in the kernel called "__mcount_loc". This will hold a list of pointers to the mcount relocation for each call site of mcount. For example: objdump -dr init/main.o [...] Disassembly of section .text: 0000000000000000 <do_one_initcall>: 0: 55 push %rbp [...] 000000000000017b <init_post>: 17b: 55 push %rbp 17c: 48 89 e5 mov %rsp,%rbp 17f: 53 push %rbx 180: 48 83 ec 08 sub $0x8,%rsp 184: e8 00 00 00 00 callq 189 <init_post+0xe> 185: R_X86_64_PC32 mcount+0xfffffffffffffffc [...] We will add a section to point to each function call. .section __mcount_loc,"a",@progbits [...] .quad .text + 0x185 [...] The offset to of the mcount call site in init_post is an offset from the start of the section, and not the start of the function init_post. The mcount relocation is at the call site 0x185 from the start of the .text section. .text + 0x185 == init_post + 0xa We need a way to add this __mcount_loc section in a way that we do not lose the relocations after final link. The .text section here will be attached to all other .text sections after final link and the offsets will be meaningless. We need to keep track of where these .text sections are. To do this, we use the start of the first function in the section. do_one_initcall. We can make a tmp.s file with this function as a reference to the start of the .text section. .section __mcount_loc,"a",@progbits [...] .quad do_one_initcall + 0x185 [...] Then we can compile the tmp.s into a tmp.o gcc -c tmp.s -o tmp.o And link it into back into main.o. ld -r main.o tmp.o -o tmp_main.o mv tmp_main.o main.o But we have a problem. What happens if the first function in a section is not exported, and is a static function. The linker will not let the tmp.o use it. This case exists in main.o as well. Disassembly of section .init.text: 0000000000000000 <set_reset_devices>: 0: 55 push %rbp 1: 48 89 e5 mov %rsp,%rbp 4: e8 00 00 00 00 callq 9 <set_reset_devices+0x9> 5: R_X86_64_PC32 mcount+0xfffffffffffffffc The first function in .init.text is a static function. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices The lowercase 't' means that set_reset_devices is local and is not exported. If we simply try to link the tmp.o with the set_reset_devices we end up with two symbols: one local and one global. .section __mcount_loc,"a",@progbits .quad set_reset_devices + 0x10 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices U set_reset_devices We still have an undefined reference to set_reset_devices, and if we try to compile the kernel, we will end up with an undefined reference to set_reset_devices, or even worst, it could be exported someplace else, and then we will have a reference to the wrong location. To handle this case, we make an intermediate step using objcopy. We convert set_reset_devices into a global exported symbol before linking it with tmp.o and set it back afterwards. 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 T set_reset_devices 00000000000000a8 t __setup_set_reset_devices 000000000000105f t __setup_str_set_reset_devices 0000000000000000 t set_reset_devices Now we have a section in main.o called __mcount_loc that we can place somewhere in the kernel using vmlinux.ld.S and access it to convert all these locations that call mcount into nops before starting SMP and thus, eliminating the need to do this with kstop_machine. Note, A well documented perl script (scripts/recordmcount.pl) is used to do all this in one location. Signed-off-by: Steven Rostedt <srostedt@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>