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Kernel/riscv64: Don't clobber the boot info argument in enable_paging

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"register asm" variables don't preserve the register value, so the call
to calculate_physical_to_link_time_address_offset in the asm input
operands is allowed to clobber a0.
This commit is contained in:
Sönke Holz 2024-04-24 20:34:47 +02:00 committed by Andrew Kaster
parent 1127fa1e01
commit 01f1d2daaa
Notes: sideshowbarker 2024-07-17 11:34:34 +09:00 
Author: https://github.com/spholz
Commit: https://github.com/SerenityOS/serenity/commit/01f1d2daaa
Pull-request: https://github.com/SerenityOS/serenity/pull/24104
1 changed files with 3 additions and 2 deletions
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5
Kernel/Arch/riscv64/MMU.cpp
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@ -177,8 +177,9 @@ static UNMAP_AFTER_INIT void setup_kernel_page_directory(u64* root_table)
// This function has to fit into one page as it will be identity mapped.
[[gnu::aligned(PAGE_SIZE)]] [[noreturn]] UNMAP_AFTER_INIT static void enable_paging(BootInfo const& info, FlatPtr satp, u64* enable_paging_pte)
{
// Switch current root page table to argument 0. This will immediately take effect, but we won't not crash as this function is identity mapped.
// Switch current root page table to argument 1. This will immediately take effect, but we won't not crash as this function is identity mapped.
// Also, set up a temporary trap handler to catch any traps while switching page tables.
auto offset = calculate_physical_to_link_time_address_offset();
register FlatPtr a0 asm("a0") = bit_cast<FlatPtr>(&info);
asm volatile(
" lla t0, 1f \n"
@ -213,7 +214,7 @@ static UNMAP_AFTER_INIT void setup_kernel_page_directory(u64* root_table)
" wfi \n"
" j 1b \n"
:
: "r"(a0), [satp] "r"(satp), [offset] "r"(calculate_physical_to_link_time_address_offset()), [enable_paging_pte] "r"(enable_paging_pte)
: "r"(a0), [satp] "r"(satp), [offset] "r"(offset), [enable_paging_pte] "r"(enable_paging_pte)
: "t0");
VERIFY_NOT_REACHED();