[PATCH v2 19/21] riscv: linker script: create separate PT_LOAD segments for text, rodata, and data

[Sascha Hauer]

Fix the linker script to generate three distinct PT_LOAD segments with
correct permissions instead of combining .rodata with .data.

Before this fix, the linker auto-generated only two PT_LOAD segments:
1. Text segment (PF_R|PF_X)
2. Data segment (PF_R|PF_W) - containing .rodata, .data, .bss, etc.

This caused .rodata to be mapped with write permissions when
riscv_mmu_setup_from_elf() or riscv_pmp_setup_from_elf() set up memory
permissions based on ELF segments, defeating the W^X protection.

With explicit PHDRS directives, we now generate three segments:
1. text segment (PF_R|PF_X): .text and related code sections
2. rodata segment (PF_R): .rodata and related read-only sections
3. data segment (PF_R|PF_W): .data, .bss, and related sections

This ensures riscv_mmu_setup_from_elf() and riscv_pmp_setup_from_elf()
correctly map .rodata as read-only instead of read-write.

Also update the prelink script to handle binaries without a PT_DYNAMIC
segment, as the new PHDRS layout may result in this case.

Signed-off-by: Sascha Hauer <s.hauer at pengutronix.de>
---
 arch/riscv/lib/barebox.lds.S | 37 ++++++++++++++++++++++++-------------
 scripts/prelink-riscv.inc    |  9 +++++++--
 2 files changed, 31 insertions(+), 15 deletions(-)

diff --git a/arch/riscv/lib/barebox.lds.S b/arch/riscv/lib/barebox.lds.S
index 38376befe9a82ead2152f8c7fc581eb5bb35fab4..1565a6fedef1ade7687740240bc36f407ca880fc 100644
--- a/arch/riscv/lib/barebox.lds.S
+++ b/arch/riscv/lib/barebox.lds.S
@@ -17,14 +17,22 @@ OUTPUT_ARCH(BAREBOX_OUTPUT_ARCH)
 ENTRY(start)
 OUTPUT_FORMAT(BAREBOX_OUTPUT_FORMAT)
 
+PHDRS
+{
+	text PT_LOAD FLAGS(5);     /* PF_R | PF_X */
+	rodata PT_LOAD FLAGS(4);   /* PF_R */
+	data PT_LOAD FLAGS(6);     /* PF_R | PF_W */
+	dynamic PT_DYNAMIC FLAGS(6); /* PF_R | PF_W */
+}
+
 SECTIONS
 {
 	. = 0x0;
 
-	.image_start : { *(.__image_start) }
+	.image_start : { *(.__image_start) } :text
 
 	. = ALIGN(4);
-	._text : { *(._text) }
+	._text : { *(._text) } :text
 	.text      :
 	{
 		_stext = .;
@@ -36,44 +44,47 @@ SECTIONS
 		KEEP(*(.text_exceptions*))
 		__exceptions_stop = .;
 		*(.text*)
-	}
+	} :text
 	BAREBOX_BARE_INIT_SIZE
 
-	. = ALIGN(4);
+	. = ALIGN(4096);
 	__start_rodata = .;
 	.rodata : {
 		*(.rodata*)
 		RO_DATA_SECTION
-	}
+	} :rodata
 
 	__end_rodata = .;
 	_etext = .;
 	_sdata = .;
 
-	. = ALIGN(4);
-	.data : { *(.data*) }
+	. = ALIGN(4096);
+
+	.data : { *(.data*) } :data
 
 	/DISCARD/ : { *(.rela.plt*) }
 	.rela.dyn : {
 		__rel_dyn_start = .;
 		*(.rel*)
 		__rel_dyn_end = .;
-	}
+	} :data
 
 	.dynsym : {
 		__dynsym_start = .;
 		*(.dynsym)
 		__dynsym_end = .;
-	}
+	} :data
+
+	.dynamic : { *(.dynamic) } :data :dynamic
 
 	_edata = .;
 
-	.image_end : { *(.__image_end) }
+	.image_end : { *(.__image_end) } :data
 
 	. = ALIGN(4);
-	.__bss_start :  { *(.__bss_start) }
-	.bss : { *(.bss*) }
-	.__bss_stop :  { *(.__bss_stop) }
+	.__bss_start :  { *(.__bss_start) } :data
+	.bss : { *(.bss*) } :data
+	.__bss_stop :  { *(.__bss_stop) } :data
 	_end = .;
 	_barebox_image_size = __bss_start;
 }
diff --git a/scripts/prelink-riscv.inc b/scripts/prelink-riscv.inc
index f2b5467f5b3c19be285153d3ad7cdb210a24a94c..8a54a9737fe73827ad8cab01a61fbecc68a1140a 100644
--- a/scripts/prelink-riscv.inc
+++ b/scripts/prelink-riscv.inc
@@ -61,8 +61,13 @@ static void prelink_bonn(void *data)
 		}
 	}
 
-	if (dyns == NULL)
-		die("No dynamic section found");
+	if (dyns == NULL) {
+		/* No PT_DYNAMIC segment found - binary may not need prelinking.
+		 * This can happen with statically-linked relocatable binaries
+		 * that handle relocations differently. Exit successfully.
+		 */
+		return;
+	}
 
 	Elf_Rela *rela_dyn = NULL;
 	size_t rela_count = 0;

-- 
2.47.3