From: Michael Brown <mcb30@ipxe.org>
Date: Thu, 1 May 2025 13:24:33 +0000 (+0100)
Subject: [riscv] Allow for a non-zero link-time address
X-Git-Tag: rolling/bin~331
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=dad20602609438e72f2fe8d9dd49b9a92b8490fa;p=thirdparty%2Fipxe.git

[riscv] Allow for a non-zero link-time address

Using paging (rather than relocation records) will be easier on 64-bit
RISC-V if we place iPXE within the negative (kernel) virtual address
space.

Allow the link-time address to be non-zero and to vary between 32-bit
and 64-bit builds.  Choose addresses that are expected to be amenable
to the use of paging.

There is no particular need to use a non-zero address in the 32-bit
builds, but doing so allows us to validate that the relocation code is
handling this case correctly.

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

diff --git a/src/arch/riscv/scripts/sbi.lds b/src/arch/riscv/scripts/sbi.lds
index afb1902e1..f882f235e 100644
--- a/src/arch/riscv/scripts/sbi.lds
+++ b/src/arch/riscv/scripts/sbi.lds
@@ -5,10 +5,8 @@
 
 SECTIONS {
 
-    /* Start at virtual address zero */
-    . = 0;
-
     /* Weak symbols that need zero values if not otherwise defined */
+    saved_pos = .;
     .weak 0x0 : {
 	_weak = .;
 	*(.weak)
@@ -16,6 +14,7 @@ SECTIONS {
 	_eweak = .;
     }
     _assert = ASSERT ( ( _weak == _eweak ), ".weak is non-zero length" );
+    _assert = ASSERT ( ( . == saved_pos ), ".weak altered current position" );
 
     /* Prefix code */
     .prefix : {
@@ -105,7 +104,7 @@ SECTIONS {
     _ereloc = ( _reloc + __load_stop_reladyn - __load_start_reladyn );
 
     /* Length of initialised data */
-    _sbi_filesz = ABSOLUTE ( _ereloc );
+    _sbi_filesz = ( ABSOLUTE ( _ereloc ) - ABSOLUTE ( _prefix ) );
 
     /* Unwanted sections */
     /DISCARD/ : {
diff --git a/src/arch/riscv32/Makefile.sbi b/src/arch/riscv32/Makefile.sbi
index d62287770..5841dd4b5 100644
--- a/src/arch/riscv32/Makefile.sbi
+++ b/src/arch/riscv32/Makefile.sbi
@@ -1,5 +1,13 @@
 # -*- makefile -*- : Force emacs to use Makefile mode
 
+# Set base virtual address to 0xeb000000
+#
+# This is aligned to a 4MB boundary and so allows 4MB megapages to be
+# used to map the iPXE binary.  The address pattern is also easily
+# recognisable if leaked to unexpected contexts.
+#
+LDFLAGS		+= --section-start=.prefix=0xeb000000
+
 # Include generic SBI Makefile
 #
 MAKEDEPS	+= arch/riscv/Makefile.sbi
diff --git a/src/arch/riscv64/Makefile.sbi b/src/arch/riscv64/Makefile.sbi
index d62287770..0f7e1c373 100644
--- a/src/arch/riscv64/Makefile.sbi
+++ b/src/arch/riscv64/Makefile.sbi
@@ -1,5 +1,13 @@
 # -*- makefile -*- : Force emacs to use Makefile mode
 
+# Set base virtual address to 0xffffffffeb000000
+#
+# This is aligned to a 2MB boundary and so allows 2MB megapages to be
+# used to map the iPXE binary.  The address pattern is also easily
+# recognisable if leaked to unexpected contexts.
+#
+LDFLAGS		+= --section-start=.prefix=0xffffffffeb000000
+
 # Include generic SBI Makefile
 #
 MAKEDEPS	+= arch/riscv/Makefile.sbi