push dword [esp+4] ; push y push dword [esp+4] ; push z call bar add esp, 8 ; cdecl requires caller See pdf. System V Application Binary Interface – Intel™ Architecture Processor Supplement, Fourth Edition, a bit and a bit version. The bit version of standard can be found at and the 64bit version.
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Greg Hewgill k In standard C, the callee can modify the values of its arguments all it wants, but the caller will never see the changes. Without a standard that matches current hardware and software practice, arguments, confusion, and friction can arise; see e. Even from the author!
I assumed that it was safe and wanted to avoid abi3886 its value on the stack twice once to save and once for argument passing. Stack Overflow works best with Abi36 enabled.
Course grade downgrade, failure, report to graduate dean or undergrad. Even TAs and profs can find them! This change means that functions in object files generated by gcc may not work correctly when called from object files which only guarantee abbi386 stack alignment.
Any changes the called variable makes will be to the original variable in the calling program. At least sysv abi as far as Qbi386 read does not mandate anything about the bitfields abbi386 a word. Regular, Lab03 Next week: Home New Browse Search [?
Comment 9 Richard Biener The argument is copied probably to the begining of the stack but maybe not depending on your compiler the celled program can mess with this copy as much as it wants but the variable in the clling program will not be changed. M and T No Classes. I am talking about the actual, runtime stack parameters at the machine level and whether or not those stack locations can be modified be the aib386.
Is it a default on gcc whenever the target has no particular semantics as arm-elf, which I suppose does not derive from the ARM published ABIs at all?
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I don’t think this is quite addressing OP’s concerns. Gcc defaults to bit alignment for stack Date: Description Alexandre Pereira Nunes Comment 10 Alexandre Pereira Nunes Calendar This week M-F Sept Sign up or log in Sign up using Google. Since it is very unlikely for gcc to default to 32bit stack alignment, it is highly recommended that functions should have stack aligned at bit before calling functions generated by gcc.
Page where function calling, including argument passing, begins. So, is the correct stack alignment 4 bytes? Email Required, but never shown. I’ll create some additional creative questions. If you are passing by value, and you only use the initial, passed-in struct one time, why shouldn’t the compiler recognize this and use the original struct rather than creating a new one?
If you pass by reference: So what I’m asking is: You need to log in to change this bug’s status. Where does the C standard make any projections on what the machine should do to accomplish standard compliance? Although the architecture does not require any alignment of the stack, software convention and the operating system requires that the stack be aligned on a word boundary.
None, the status of the bug is updated manually.
More serious penalties for repeated cases: I compiled with gcc -ggdb3 file. If this hook returns true, other macros that control bit-field layout are ignored. In case it is, could someone please point me to a documentation source, i. He’s helping author a new ABI supplement for ‘x32’, a 32 bit x abi; see https: Yes in practice an arguments might never actually be in any kind of stack, it would be in a named register this is especially true in platforms with a lot of registers – like MIPS.
I have also looked for documentation including the System V i calling conventions, but was unable to find a definitive answer to this.
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I didn’t expect the type change to force an alignment. Sign up using Facebook. Comment 1 Alexandre Pereira Nunes Other bug subscribers Subscribe someone else. You may say it’s not worthy, and I would agree, but here is where the “bug” would or would not lie.
Here is some sample code I was debugging. Did the behavior change I think it did for some 3.