Hi all, I'm looking into reviving the efforts to port gcc to VideoCore IV [1]. One issue I've run into is the need to find out target branch distance at compile time. I looked around, and it's not the first one architecture with such requirement, but AFAICS it has never been solved properly.
For example, AVR tracks instruction length. Later, ret_cond_branch() selects between a branch instruction and an inverted branch followed by an unconditional jump based on these calculated lengths. This works great ... until there's some inline asm() statement, for which gcc cannot keep track of the length attribute, so it is probably taken as zero. Linker then fails with a cryptic message: > relocation truncated to fit: R_AVR_7_PCREL against `no symbol' I can provide a minimal test case and report a bug if you want... Developers work around the issue by rewriting their code when they are bitten by this, but it is less than optimal, because you cannot really get rid of all inline assembly, and it's in general unpredictable where these inline asm() blocks will be placed by the compiler. OTOH, the avr backend is pretty outdated, so there may be a better alternative that I'm just not seeing. Any hints? Background: There is a port of the VC4 port of the LK embedded kernel [2]. I have tried to build that kernel with optimization turned on, but I'm getting: compiling kernel/thread.c /tmp/ccJFdnfX.s: Assembler messages: /tmp/ccJFdnfX.s:1451: Error: operand out of range (64 not between -64 and 63) That's because there is an inline "di" (disable interrupts) instruction inside a conditional statement in thread_yield(), which causes this off-by-one miscalculation. Petr T [1] https://github.com/itszor/gcc-vc4 [2] https://github.com/librerpi/lk
pgpRhoEcCoUru.pgp
Description: Digitálnà podpis OpenPGP
