Re: [Tinycc-devel] TCC riscv32 port - Deferring code generation on external symbol
Sam Ellicott wrote: Example code is here ``` .global _start _start: la gp, _global_pointer la a0, _bss_start la a1, _bss_end bgeu a0, a1, 2f 1: sw zero, (a0) addi a0, a0, 4 bltu a0, a1, 1b 2: # setup the stack la sp, _stack_end call main ``` For example when the `_global_pointer` symbol is encountered what is the correct behavior? Since the symbol is defined in a separate compilation unit, I'm assuming some sort of marker needs to be placed in the .o file to indicate what immediate value goes there at link time. However, I don't know what that is, or how it is generated. Similarly for `_bss_start`, `_bss_end`, etc. That 'sort of marker' thing is called 'relocation' entry. You would emit code as if it were 'la a0, 0' but put a relocation on it that refers to the symbol. (In tcc, using 'greloc[a]' for example). Whether or not the symbol is defined in the current unit doesn't really make a difference in that regard. With riscv it's maybe two relocations as I've seen that 'la' really is two instructions to first load the 20 HI-bits and then the 12 LO-bits. -- gr Thanks! ___ Tinycc-devel mailing list Tinycc-devel@nongnu.org https://lists.nongnu.org/mailman/listinfo/tinycc-devel
Re: [Tinycc-devel] TCC riscv32 port - Deferring code generation on external symbol
Example code is here ``` .global _start _start: la gp, _global_pointer la a0, _bss_start la a1, _bss_end bgeu a0, a1, 2f 1: sw zero, (a0) addi a0, a0, 4 bltu a0, a1, 1b 2: # setup the stack la sp, _stack_end call main ``` For example when the `_global_pointer` symbol is encountered what is the correct behavior? Since the symbol is defined in a separate compilation unit, I'm assuming some sort of marker needs to be placed in the .o file to indicate what immediate value goes there at link time. However, I don't know what that is, or how it is generated. Similarly for `_bss_start`, `_bss_end`, etc. Thanks! ___ Tinycc-devel mailing list Tinycc-devel@nongnu.org https://lists.nongnu.org/mailman/listinfo/tinycc-devel
Re: [Tinycc-devel] TCC riscv32 port - Deferring code generation on external symbol
Example? On April 16, 2022 5:03:59 AM UTC, Sam Ellicott wrote: >Hi All, >I have been working on porting tcc to generate code for riscv32 >targets and have run into an issue when writing the assembler in the >case of an externally defined symbol. ... ___ Tinycc-devel mailing list Tinycc-devel@nongnu.org https://lists.nongnu.org/mailman/listinfo/tinycc-devel
[Tinycc-devel] TCC riscv32 port - Deferring code generation on external symbol
Hi All, I have been working on porting tcc to generate code for riscv32 targets and have run into an issue when writing the assembler in the case of an externally defined symbol. Since the symbol will not be defined until link time I need to defer the code generation to the linking step. However, I haven't been able to ascertain 1) what to check for in a symbol that lets me know that I do not have enough information for code generation (VT_EXTERN flag?), 2) how to let the linker know where and what code it should generate to populate the symbol load. I've been poking through other architecture's code but haven't had much luck. Thanks, -Sam Ellicott Soli Deo Gloria ___ Tinycc-devel mailing list Tinycc-devel@nongnu.org https://lists.nongnu.org/mailman/listinfo/tinycc-devel
