From: Michael Brown <mcb30@ipxe.org>
Date: Thu, 1 May 2025 13:04:27 +0000 (+0100)
Subject: [riscv] Split out runtime relocator to libprefix.S
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=a4b5dd63c5a99df3cfa2c4dd3cd0fd9019635b92;p=thirdparty%2Fipxe.git

[riscv] Split out runtime relocator to libprefix.S

Split out the runtime relocation logic from sbiprefix.S to a new
library libprefix.S.

Since this logically decouples the process of runtime relocation from
the _sbi_start symbol (currently used to determine the base address
for applying relocations), provide an alternative mechanism for the
relocator to determine the base address.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
---

diff --git a/src/arch/riscv/prefix/libprefix.S b/src/arch/riscv/prefix/libprefix.S
new file mode 100644
index 000000000..7f4d57000
--- /dev/null
+++ b/src/arch/riscv/prefix/libprefix.S
@@ -0,0 +1,104 @@
+/*
+ * Copyright (C) 2025 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ *
+ * You can also choose to distribute this program under the terms of
+ * the Unmodified Binary Distribution Licence (as given in the file
+ * COPYING.UBDL), provided that you have satisfied its requirements.
+ */
+
+	FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL )
+
+/** @file
+ *
+ * RISC-V prefix library
+ *
+ */
+
+	.section ".note.GNU-stack", "", @progbits
+	.text
+
+/*****************************************************************************
+ *
+ * Apply relocation records
+ *
+ *****************************************************************************
+ *
+ * Apply relocation records from .rel.dyn to fix up iPXE to run at its
+ * current address.
+ *
+ * This function must run before .bss is zeroed (since the relocation
+ * records are overlaid with .bss).  It does not require a valid stack
+ * pointer.
+ *
+ * Parameters: none (address is implicit in the program counter)
+ *
+ * Returns: none
+ *
+ */
+
+/* Relative relocation type */
+#define R_RISCV_RELATIVE 3
+
+	/* Layout of a relocation record */
+	.struct 0
+rela_offset:	.space ( __riscv_xlen / 8 )
+rela_type:	.space ( __riscv_xlen / 8 )
+rela_addend:	.space ( __riscv_xlen / 8 )
+rela_len:
+	.previous
+
+	.section ".prefix.apply_relocs", "ax", @progbits
+	.globl	apply_relocs
+apply_relocs:
+
+	/* Get relocation records */
+	la	t0, _reloc
+	la	t1, _ereloc
+
+	/* Determine current location */
+	la	t2, reloc_base
+	LOADN	t2, (t2)
+	sub	t2, t0, t2
+
+1:	/* Read relocation record */
+	LOADN	t3, rela_offset(t0)
+	LOADN	t4, rela_type(t0)
+	LOADN	t5, rela_addend(t0)
+
+	/* Check relocation type */
+	addi	t4, t4, -R_RISCV_RELATIVE
+	bnez	t4, 2f
+
+	/* Apply relocation */
+	add	t3, t3, t2
+	add	t5, t5, t2
+	STOREN	t5, (t3)
+2:
+	/* Loop until done */
+	addi	t0, t0, rela_len
+	blt	t0, t1, 1b
+
+	/* Return to caller */
+	ret
+	.size	apply_relocs, . - apply_relocs
+
+	/* Link-time address of _reloc */
+	.section ".rodata", "a", @progbits
+reloc_base:
+	.dword	_reloc_base
+	.size	reloc_base, . - reloc_base
diff --git a/src/arch/riscv/prefix/sbiprefix.S b/src/arch/riscv/prefix/sbiprefix.S
index e8ef40b6d..ccf8b0743 100644
--- a/src/arch/riscv/prefix/sbiprefix.S
+++ b/src/arch/riscv/prefix/sbiprefix.S
@@ -41,17 +41,6 @@
 #define SBI_SRST_SYSTEM_RESET 0x00
 #define SBI_RESET_COLD 0x00000001
 
-/* Relative relocation type */
-#define R_RISCV_RELATIVE 3
-
-	/* Layout of a relocation record */
-	.struct 0
-rela_offset:	.space ( __riscv_xlen / 8 )
-rela_type:	.space ( __riscv_xlen / 8 )
-rela_addend:	.space ( __riscv_xlen / 8 )
-rela_len:
-	.previous
-
 	/*
 	 * Display progress message via debug console
 	 */
@@ -85,23 +74,7 @@ _sbi_start:
 	progress "\nSBI->iPXE"
 
 	/* Apply dynamic relocations */
-	la	t0, _reloc
-	la	t1, _ereloc
-	la	t2, _sbi_start
-1:	/* Read relocation record */
-	LOADN	t3, rela_offset(t0)
-	LOADN	t4, rela_type(t0)
-	LOADN	t5, rela_addend(t0)
-	/* Check relocation type */
-	addi	t4, t4, -R_RISCV_RELATIVE
-	bnez	t4, 2f
-	/* Apply relocation */
-	add	t3, t3, t2
-	add	t5, t5, t2
-	STOREN	t5, (t3)
-2:	/* Loop */
-	addi	t0, t0, rela_len
-	blt	t0, t1, 1b
+	call	apply_relocs
 	progress " .reloc"
 
 	/* Zero the bss */
diff --git a/src/arch/riscv/scripts/sbi.lds b/src/arch/riscv/scripts/sbi.lds
index a65b27181..afb1902e1 100644
--- a/src/arch/riscv/scripts/sbi.lds
+++ b/src/arch/riscv/scripts/sbi.lds
@@ -87,6 +87,14 @@ SECTIONS {
 	}
     }
 
+    /* Absolute link-time address of _reloc
+     *
+     * The runtime relocator needs to know the link-time addresses.
+     * Since RISC-V uses .rela (rather than .rel), the only way to
+     * expose this to the relocator is via an absolute symbol.
+     */
+    _reloc_base = ABSOLUTE ( _reloc );
+
     /* Calculate end of relocations
      *
      * This cannot be done by placing "_ereloc = .;" inside the