intel - strcmp and strcmp_sse functions in libc -

-

i've seen in libc.so actual type of strcmp_sse call decided function strcmp itself.

here code:

      strcmp:  .text:000000000007b9f0                 cmp     cs:__cpu_features.kind, 0  .text:000000000007b9f7                 jnz     short loc_7b9fe  .text:000000000007b9f9                 call    __init_cpu_features  .text:000000000007b9fe  .text:000000000007b9fe loc_7b9fe:                              ; code xref: .text:000000000007b9f7j  .text:000000000007b9fe                 lea     rax, __strcmp_sse2_unaligned  .text:000000000007ba05                 test    cs:__cpu_features.cpuid._eax, 10h  .text:000000000007ba0f                 jnz     short locret_7ba2b  .text:000000000007ba11                 lea     rax, __strcmp_ssse3  .text:000000000007ba18                 test    cs:__cpu_features.cpuid._ecx, 200h  .text:000000000007ba22                 jnz     short locret_7ba2b  .text:000000000007ba24                 lea     rax, __strcmp_sse2  .text:000000000007ba2b  .text:000000000007ba2b locret_7ba2b:                           ; code xref: .text:000000000007ba0fj  .text:000000000007ba2b                                         ; .text:000000000007ba22j  .text:000000000007ba2b                 retn

what not understand address of strcmp_sse function call placed in rax , never called. therefore wondering: going call *rax? when?

linux dynamic linker supports special symbol type called stt_gnu_ifunc. strcmp implemented ifunc. 'regular' symbols in dynamic library nothing more mapping name address. ifuncs bit more complex that: address isn't readily available, in order obtain linker must execute piece of code library itself. seeing example of such peice of code here. note in x86_64 abi function returns result in rax.

this technique typically used pick optimal implementation based on cpu features. please note selection logic runs once; first call strcmp fast.


Comments

Post a Comment

Popular posts from this blog

python - TypeError: start must be a integer -

-
i trying draw 5 turtles, getting typeerror on line 25. here code: import turtle wn = turtle.screen() redrose = turtle.turtle() color = input("what background color be?") fillcolor_f = input("what color of rose be?") redrose.hideturtle() redrose.speed(30) redrose.penup() redrose.left(180) redrose.forward(175) redrose.right(90) redrose.forward(30) redrose.right(90) redrose.pendown() def drawrose(red): redrose.color("pink") redrose.fillcolor(fillcolor_f) redrose.fill(true) in range(red): redrose.forward(i) redrose.right(49) in range(5): drawrose(redrose) redrose.penup() redrose.forward(350) redrose.right(144) redrose.pendown() redrose.fill(false) drawrose(50) wn.bgcolor(color) i trying draw 5 roses, produces errors. doing in interactivepython.org. you recursively calling drawrose wrong parameter. on line 23 ( for in range(red): ) expect red integer...
Read more

c# - DevExpress RepositoryItemComboBox BackColor property ignored -

-
i have following code almost works properly; private void cbstatus_drawitem(object sender, listboxdrawitemeventargs e) { string item = e.item string; if (item != null) { switch (item) { case "1": e.appearance.forecolor = color.green; e.appearance.backcolor = color.green; break; case "2": e.appearance.forecolor = color.orange; e.appearance.backcolor = color.orange; break; case "3": e.appearance.forecolor = color.red; e.appearance.backcolor = color.red; break; } } } when dropdown shown, items forecolor correct, backcolor remains whatever backcolor of theme is; i.e. if i've got set dark theme, backcolor dark, cells in gridview, rather being green/orange/red. i've tried setting e.appearance.options.usebackcolor trying set e....
Read more

django - Creating multiple model instances in DRF3 -

-
1) create multiple model instances 1 api call, asked here: how create multiple model instances django rest framework? tried solution named in link, no success. i trying upload multiple files in 1 api call. result: files uploaded (only once overwrote perform_create) 1 instance created (if send 2 files, latter created instance). my code: class fileuploadserializer(serializers.modelserializer): def __init__(self, *args, **kwargs): many = kwargs.pop('many', true) super(fileuploadserializer, self).__init__(many=many, *args, **kwargs) class meta: model = fileupload read_only_fields = ('created', 'datafile', 'owner') class fileuploadviewset(viewsets.modelviewset): queryset = fileupload.objects.all() serializer_class = fileuploadserializer parser_classes = (multipartparser, formparser, ) def perform_create(self, serializer): file_list = self.request.data.getlist('file') ...
Read more