On Wed, Dec 12, 2018 at 04:45:08PM +0300, Evgeny Yakovlev wrote: > Currently make_bios_writable_intel will call __make_bios_writeable_intel > from high rom memory by manually correcting its offset to make sure that > we safely execute it while overriding memory mapping through PAMs > > However we still may call code from low memory, when > __make_bios_writeable_intel itself calls other code without manual > pointer adjustments. Right now it calls pci_config_readl and > pci_config_writel. > > Consider this scenario: > 0. Linker puts pci_config_writel in F-segment. > 1. first pci_config_writel is called to reprogram PAM0-3, which means > remap regions 0xF0000-0xFFFFF and 0xD0000 - 0xC7FFF. > 2. second pci_config_writel is called to reprogram PAM4-7 but code in > F-segment is no longer valid, including pci_config_writel.
The x86 instruction set uses relative function calls by default. So, a call to pci_config_writel() calls the copy of that function also located in 0xFFF00000. Are you seeing an error in practice? It's known that __make_bios_writeable_intel() is an ugly hack - it's there because qemu doesn't support "write back" mode of the pam registers. So the code needs to run at a different location when making that area writable. It is specific to qemu, so we only need it to run okay on qemu. -Kevin _______________________________________________ SeaBIOS mailing list SeaBIOS@seabios.org https://mail.coreboot.org/mailman/listinfo/seabios
