Re: [PATCH v3 17/23] ARM: PBL: setup MMU with proper permissions from ELF segments

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hi,

On 1/8/26 4:50 PM, Sascha Hauer wrote:
> Move complete MMU setup into PBL by leveraging ELF segment information
> to apply correct memory permissions before jumping to barebox proper.
> 
> After ELF relocation, parse PT_LOAD segments and map each with
> permissions derived from p_flags:
> - Text segments (PF_R|PF_X): Read-only + executable (MAP_CODE)
> - Data segments (PF_R|PF_W): Read-write (MAP_CACHED)
> - RO data segments (PF_R): Read-only (ARCH_MAP_CACHED_RO)

MAP_CACHED_RO is the name now.

> -static inline void remap_range_end_sans_text(unsigned long start, unsigned long end,
> +static inline void remap_range_end_sans_image(unsigned long start, unsigned long end,
>  					     unsigned map_type)
>  {
> -	unsigned long text_start = (unsigned long)&_stext;
> -	unsigned long text_end = (unsigned long)&_etext;
> +	unsigned long image_start = (unsigned long)&_stext;
> +	unsigned long image_end = (unsigned long)&_etext;

Uhm, __image_start and __image_end, not just the variable names...

> +	/*
> +	 * Now that the ELF image is relocated, we know the exact addresses
> +	 * of all segments. Set up MMU with proper permissions based on
> +	 * ELF segment flags (PF_R/W/X).
> +	 */
> +	if (IS_ENABLED(CONFIG_MMU)) {
> +		ret = pbl_mmu_setup_from_elf(&elf, membase, memsize);

Add static inline stub to header for !MMU case and drop IS_ENABLED() here?

> +		if (ret) {
> +			pr_err("Failed to setup MMU from ELF: %d\n", ret);
> +			hang();

panic()

> +int pbl_mmu_setup_from_elf(struct elf_image *elf, unsigned long membase,
> +			    unsigned long memsize)
> +{
> +	void *phdr;
> +	int i;
> +	int phnum = elf_hdr_e_phnum(elf, elf->hdr_buf);
> +	size_t phoff = elf_hdr_e_phoff(elf, elf->hdr_buf);
> +	size_t phentsize = elf_size_of_phdr(elf);
> +
> +	pr_debug("Setting up MMU from ELF segments\n");
> +	pr_debug("ELF entry point: 0x%llx\n", elf->entry);

Drop this line as CONFIG_DEBUG_PBL enables all pr_debug and this line
would then be duplicate.

> +		/* Validate alignment - warn and round if needed */
> +		if (!IS_ALIGNED(addr, PAGE_SIZE) || !IS_ALIGNED(size, PAGE_SIZE)) {

Remove IS_ALIGNED(addr, PAGE_SIZE) as it's not rounded and the message
is thus not accurate. We shouldn't round it either, just falling through
to remapping will raise a panic if it's unaligned, which is ok IMO.


> +		pbl_remap_range((void *)addr, addr, size, mmu_flags);

Using remap_range() means we can avoid the (void *)addr.

Cheers,
Ahmad

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