tls: parameterize static tls reservation

This patch makes it possible to pass size of the app static TLS reservation as build parameter to makefile. It also adds logic calculate what value of this parameter should be if the resevation is too small for given app. Signed-off-by: Waldemar Kozaczuk <[email protected]>
cloudius-systems · Nov 7, 2019 · 2d5f2d5 · 2d5f2d5
1 parent b0478df
commit 2d5f2d5
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Showing 5 changed files with 21 additions and 9 deletions.
diff --git a/Makefile b/Makefile
@@ -424,6 +424,10 @@ kernel_base := 0x200000
 lzkernel_base := 0x100000
 kernel_vm_base := 0x40200000
 
+# the default of 64 bytes can be overridden by passing the app_local_exec_tls_size
+# environment variable to the make or scripts/build
+app_local_exec_tls_size := 0x40
+
 $(out)/arch/x64/boot16.o: $(out)/lzloader.elf
 $(out)/boot.bin: arch/x64/boot16.ld $(out)/arch/x64/boot16.o
 	$(call quiet, $(LD) -o $@ -T $^, LD $@)
@@ -1886,7 +1890,7 @@ stage1: $(stage1_targets) links
 
 $(out)/loader.elf: $(stage1_targets) arch/$(arch)/loader.ld $(out)/bootfs.o
 	$(call quiet, $(LD) -o $@ --defsym=OSV_KERNEL_BASE=$(kernel_base) \
-	    --defsym=OSV_KERNEL_VM_BASE=$(kernel_vm_base) --defsym=OSV_KERNEL_VM_SHIFT=$(kernel_vm_shift) \
+	    --defsym=OSV_KERNEL_VM_BASE=$(kernel_vm_base) --defsym=OSV_KERNEL_VM_SHIFT=$(kernel_vm_shift) --defsym=APP_LOCAL_EXEC_TLS_SIZE=$(app_local_exec_tls_size) \
 		-Bdynamic --export-dynamic --eh-frame-hdr --enable-new-dtags \
 	    $(^:%.ld=-T %.ld) \
 	    --whole-archive \

diff --git a/arch/aarch64/loader.ld b/arch/aarch64/loader.ld
@@ -108,7 +108,7 @@ SECTIONS
         *(.tbss .tbss.* .gnu.linkonce.tb.*) *(.tcommon)
         _pie_static_tls_start = .;
         /* This is a reserve intended for executables' (pie or non-pie) TLS block */
-        . = . + 64;
+        . = . + APP_LOCAL_EXEC_TLS_SIZE;
         _pie_static_tls_end = .;
     } : tls : text
     .tls_template_size = SIZEOF(.tdata) + SIZEOF(.tbss);

diff --git a/arch/x64/loader.ld b/arch/x64/loader.ld
@@ -92,7 +92,7 @@ SECTIONS
         *(.tbss .tbss.* .gnu.linkonce.tb.*)
         _pie_static_tls_start = .;
         /* This is a reserve intended for executables' (pie or non-pie) TLS block */
-        . = . + 64;
+        . = . + APP_LOCAL_EXEC_TLS_SIZE;
         . = ALIGN(64);
         _pie_static_tls_end = .;
     } :tls :text

diff --git a/core/elf.cc b/core/elf.cc
@@ -471,13 +471,20 @@ void object::load_segments()
         abort("Statically linked executables are not supported!\n");
     }
     if (_is_executable && _tls_segment) {
-        auto needed_tls_size = get_aligned_tls_size();
+        auto app_tls_size = get_aligned_tls_size();
         ulong pie_static_tls_maximum_size = &_pie_static_tls_end - &_pie_static_tls_start;
-        if (needed_tls_size > pie_static_tls_maximum_size) {
-            std::cout << "WARNING: " << pathname() << " is a PIE using TLS of size " << needed_tls_size
-                  << " which is greater than " << pie_static_tls_maximum_size << " bytes limit. "
-                  << "Either increase the size of TLS reserve in arch/x64/loader.ld or "
-                  << "link with '-shared' instead of '-pie'.\n";
+        if (app_tls_size > pie_static_tls_maximum_size) {
+            // The reservation at the end of the kernel TLS is NOT big enough
+            // to hold the app static TLS. Let us calculate what the reservation should be
+            // and inform user how to relink kernel
+            auto kernel_tls_size = sched::kernel_tls_size();
+            auto kernel_tls_used_size = kernel_tls_size - pie_static_tls_maximum_size;
+            auto kernel_tls_needed_size = align_up(kernel_tls_used_size + app_tls_size, 64UL);
+            auto app_tls_needed_size = kernel_tls_needed_size - kernel_tls_used_size;
+            std::cout << "WARNING: " << pathname() << " is a PIE using TLS of size " << app_tls_size
+                  << " which is greater than the " << pie_static_tls_maximum_size << " bytes limit. "
+                  << "Either re-link the kernel by adding 'app_local_exec_tls_size=" << app_tls_needed_size
+                  << "' to ./scripts/build or re-link the app with '-shared' instead of '-pie'.\n";
         }
     }
 }

diff --git a/scripts/build b/scripts/build
@@ -28,6 +28,7 @@ usage() {
 	  fs=zfs|rofs|ramfs             Specify the filesystem of the image partition
 	  fs_size=N                     Specify the size of the image in bytes
 	  fs_size_mb=N                  Specify the size of the image in MiB
+	  app_local_exec_tls_size=N     Specify the size of app local TLS in bytes; the default is 64
 	  usrskel=<*.skel>              Specify the base manifest for the image
 	  <module_makefile_arg>=<value> Pass value of module_makefile_arg to an app/module makefile
 	                                (can be used to customize specific app/module build process)