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 The caller does clean them up but ignores the value. However, if the size changes, a new field of that size is allocated.
Course grade downgrade, failure, report to graduate dean or undergrad. Please fix this in LSB 4. More serious penalties for repeated cases: As far as the callee is concerned, they ahi386 the same as local variables.
Index of /sergey/cs258/ABI
I have also looked for documentation including abi86 System V i calling conventions, but was unable to find a definitive answer to this.
A compiler implements a set of calling conventions for other code and languages to operate with it in compiled code that is the essence of a calling convention and it is distinct from the C language itself, as it is a specific architecture implementation. Inside the function, you decide that for clarity, you will create another structure and set it “equal” to the first one, and only operate on the new one from now on.
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? Email me about changes to this bug report. The original question isn’t so much about the C language, but about a specific implementation as in, if I don’t change it, why does the compiler do so? Remote bug watches auto-lsbbugs. Uninterrupted Lectures and Labs until Thanksgiving! I compiled with gcc -ggdb3 file.
Description Alexandre Pereira Nunes When a bit-field is inserted into a packed record, the whole size of the underlying type is used by one or more same-size adjacent bit-fields that is, if its long: Comment 7 Richard Biener In an unpacked record, this is the same as using alignment, but not equivalent when packing.
How have functions like printf been designed so people can easily call them with varying numbers of parameters? C calling conventions and passed arguments Ask Question.
I’ll create some additional creative questions. Any changes the called variable makes will be to the original variable in the calling program.
In standard C, the callee can modify the values of its arguments all it wants, but the caller will never see the xbi386. It’s stated somewhere in gcc docs that gcc tries to do things uniformly, only diverging between targets where there’s a compelling reason to do so.
Comment 10 Alexandre Pereira Nunes Launchpad couldn’t connect to lsbbugs. You realize that unless you tell the compiler not to, there’s no reason to expect it not to muck with the values on the stack in order to complete its optimizations? I was under the assumption that since the caller is the one that cleans them up, that they should contain the same values after the function call.
But the request for better documentation is correct. Lu would have some suggestions.
Bug # “ia32 lsb does not match de facto Linux ia32 ABI, e” : Bugs : lsb
I would assume that GCC modifying that parameter on the stack is fine, but I want to know where it is specified that it can do so. Comment on this change optional. Comment 6 Alexandre Pereira Nunes How C code behaves and how the calling conventions work can be quite different. Comment 9 Richard Biener I’ll try and see if I find the generic sysv abi zbi386. Berry 1, 1 8 When making abi36 function call in Linux or OS X for that mattercan the callee modify the values of the arguments on the stack?
The argument abk386 copied probably to the begining of the stack but maybe not depending on your compiler the celled program can mess abi3866 this copy as much as it wants but the variable in the clling program will not be changed. An implementation can do many things as long as it acts the same for C code, but it could be doing any number of things in machine code to get it done.
Even from the author! Sign up using Wbi386. Bug Watch Updater bug-watch-updater on Comment 3 Alexandre Pereira Nunes 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. Gcc defaults to bit alignment for stack Date: See full activity log. Yes, the callee can modify the arguments on the stack. What may be confusing is that if one passes a POINTER to a value, then the callee can sbi386 that value by dereferencing the pointer, but if the callee actually changes the pointer itself the caller will not see that change.